Democratic Peace Theory


Democratic peace theory posits that democracies are hesitant to engage in armed conflict with other identified democracies. In contrast to theories explaining war engagement, it is a ‘Theory Of Peace’ outlining motives that dissuade state-sponsored violence. Some theorists prefer terms such as ‘mutual democratic pacifism’ or ‘inter-democracy nonaggression hypothesis’ so as to clarify that a state of peace is not singular to democracies, but rather that it is easily sustained between democratic nations. Several factors are held as motivating peace between liberal states:

Democratic leaders are forced to accept culpability for war losses to a voting public; Publicly accountable statesmen are more inclined to establish diplomatic institutions for resolving international tensions; Democracies are less inclined to view countries with adjacent policy and governing doctrine as hostile; and Democracies tend to possess greater public wealth than other states, and therefore eschew war to preserve infrastructure and resources. 

Physicist and historian Spencer R. Weart disputes this last claim, stating, ‘It is not because of their advanced economic development—wealthy countries fight wars about as often as poor ones.’ Critics of Democratic Peace Theory argue that it conflates correlation with causation, and that the academic definitions of ‘democracy’ and ‘war’ can be manipulated so as to manufacture an artificial trend.

Though the democratic peace theory was not rigorously or scientifically studied until the 1960s, the basic principles of the concept had been argued as early as the 1700s in the works of philosopher Immanuel Kant and political theorist Thomas Paine. Kant foreshadowed the theory in his essay ‘Perpetual Peace’ written in 1795, although he thought that a world with only constitutional republics was only one of several necessary conditions for a perpetual peace. Kant’s theory was that a majority of the people would never vote to go to war, unless in self-defense. Therefore, if all nations were republics, it would end war, because there would be no aggressors. In earlier but less cited works, Thomas Paine made similar or stronger claims about the peaceful nature of republics. Paine wrote in ‘Common Sense’ in 1776: ‘The Republics of Europe are all (and we may say always) in peace.’ Paine argued that kings would go to war out of pride in situations where republics would not. ‘Democracy in America’ (1835-1840), by French historian and social scientist Alexis de Tocqueville, also argued that democratic nations were less likely to wage war.

Research on the democratic peace theory has to define ‘democracy’ and ‘peace’ (or, more often, ‘war’). Similarly, the main criticism contends that the theory is an example of equivocation, particularly, the ‘No true Scotsman fallacy’ (modifying the subject of the assertion to exclude the specific case or others like it by rhetoric, without reference to any specific objective rule). Democracies have been defined differently by different theorists and researchers; this accounts for some of the variations in their findings. Some examples: Small and Singer (1976) define democracy as a nation that (1) holds periodic elections in which the opposition parties are as free to run as government parties, (2) allows at least 10% of the adult population to vote, and (3) has a parliament that either controls or enjoys parity with the executive branch of the government. Doyle (1983) requires (1) that ‘liberal régimes’ have market or private property economics, (2) they have policies that are internally sovereign, (3) they have citizens with juridical rights, and (4) they have representative governments. Either 30% of the adult males were able to vote or it was possible for every man to acquire voting rights as by attaining enough property. He allows greater power to hereditary monarchs than other researchers; for example, he counts the rule of Louis-Philippe of France as a liberal régime.

Ray (1995) requires that at least 50% of the adult population is allowed to vote and that there has been at least one peaceful, constitutional transfer of executive power from one independent political party to another by means of an election. This definition excludes long periods often viewed as democratic. For example, the United States until 1800, India from independence until 1979, and Japan until 1993 were all under one-party rule, and thus would not be counted under this definition. Rummel (1997) states that ‘By democracy is meant liberal democracy, where those who hold power are elected in competitive elections with a secret ballot and wide franchise (loosely understood as including at least 2/3 of adult males); where there is freedom of speech, religion, and organization; and a constitutional framework of law to which the government is subordinate and that guarantees equal rights.’

The above definitions are binary, classifying nations into either democracies or nondemocracies. Many researchers have instead used more finely grained scales. One example is the Polity data series which scores each state on two scales, one for democracy and one for autocracy, for each year since 1800; as well as several others. The use of the Polity Data has varied. Some researchers have done correlations between the democracy scale and belligerence; others have treated it as a binary classification by (as its maker does) calling all states with a high democracy score and a low autocracy score democracies; yet others have used the difference of the two scores, sometimes again making this into a binary classification.

Several researchers have observed that many of the possible exceptions to the democratic peace have occurred when at least one of the involved democracies was very young. Many of them have therefore added a qualifier, typically stating that the peacefulness apply to democracies older than three years. Rummel (1997) argues that this is enough time for ‘democratic procedures to be accepted, and democratic culture to settle in.’ Additionally, this may allow for other states to actually come to the recognition of the state as a democracy. Mansfield and Snyder (2002, 2005), while agreeing that there have been no wars between mature liberal democracies, state that countries in transition to democracy are especially likely to be involved in wars. They find that democratizing countries are even more warlike than stable democracies, stable autocracies or even countries in transition towards autocracy. So, they suggest caution in eliminating these wars from the analysis, because this might hide a negative aspect of the process of democratization.

Quantitative research on international wars usually define war as a military conflict with more than 1000 killed in battle in one year. This is the definition used in the ‘Correlates of War Project’ which has also supplied the data for many studies on war. Some researchers have used different definitions. For example, Weart (1998) defines war as more than 200 battle deaths. Russett, when looking at Ancient Greece, only requires some real battle engagement, involving on both sides forces under state authorization. Militarized Interstate Disputes (MIDs), in the ‘Correlates of War Project’ classification, are lesser conflicts than wars. Such a conflict may be no more than military display of force with no battle deaths. MIDs and wars together are ‘militarized interstate conflicts’ or MICs. MIDs include the conflicts that precede a war; so the difference between MIDs and MICs may be less than it appears. Statistical analysis and concerns about degrees of freedom are the primary reasons for using MID’s instead of actual wars. Wars are relatively rare. An average ratio of 30 MIDs to one war provides a richer statistical environment for analysis.

Most research is regarding the dyadic peace, that democracies do not fight one another. Very few researchers have supported the monadic peace, that democracies are more peaceful in general. There are some recent papers that find a slight monadic effect. Müller and Wolff (2004), in listing them, agree ‘that democracies on average might be slightly, but not strongly, less warlike than other states,’ but general ‘monadic explanations is neither necessary nor convincing.’ They note that democracies have varied greatly in their belligerence against non-democracies.

Some scholars support democratic peace on probabilistic grounds: since many wars have been fought since democracies first arose, we might expect a proportionate number of wars to have occurred between democracies, if democracies fought each other as freely as other pairs of states; but proponents of democratic peace theory claim that the number is much less than might be expected. However, opponents of the theory argue this is mistaken and claim there are numerous examples of wars between democracies. Historically, cases commonly cited as exceptions include the Sicilian Expedition, the Spanish-American War, the Continuation War and more recently the Kargil War between India and Pakistan in 1999. Doyle (1983) cites the Paquisha War between Equator and Peru in 1981 and the Lebanese air force’s intervention in the Six Day War in Israel in 1967. The total number of cases suggested in the literature is at least 50.

The data set Bremer (1993) was using showed one exception, the French-Thai War of 1940; Gleditsch (1995) sees the state of war between Finland and UK during World War II, as a special case, which should probably be treated separately: an incidental state of war between democracies during large multi-polar wars. However, the UK did bomb Finland implying the war was not only on paper. Page Fortna (2004) discusses the 1974 Turkish invasion of Cyprus and the Kargil War as exceptions, finding the latter to be the most significant. However, the status of these countries as being truly democratic is a matter of debate. Limiting the theory to only truly stable and genuine democracies leads to a very restrictive set of highly prosperous nations with little incentive in armed conflict that might harm their economies, in which the theory might be expected to hold virtually by definition. Even by such stringent conditions there are still somewhat surprisingly several contradictory examples, such as the Continuation War, involving Finland and the UK.

One advocate of the democratic peace explains that his reason to choose a definition of democracy sufficiently restrictive to exclude all wars between democracies are what ‘might be disparagingly termed public relations’: students and politicians will be more impressed by such a claim than by claims that wars between democracies are less likely. One problem with the research on wars is that, as realist political scientist John Mearsheimer put it, ‘democracies have been few in number over the past two centuries, and thus there have been few opportunities where democracies were in a position to fight one another.’ Especially if using a strict definition of democracy, as by those finding no wars. Democracies have been very rare until recently. Even looser definitions of democracy, such as Doyle’s, find only a dozen democracies before the late nineteenth century, and many of them short-lived or with limited franchise. Freedom House finds no independent state with universal suffrage in 1900.

Wayman (1998), a supporter of the theory, states that ‘If we rely solely on whether there has been an inter-democratic war, it is going to take many more decades of peace to build our confidence in the stability of the democratic peace.’ Many researchers have reacted to this limitation by studying lesser conflicts instead, since they have been far more common. There have been many more MIDs than wars; the ‘Correlates of War Project’ counts several thousand during the last two centuries. A review in 2003 lists many studies that have reported that democratic pairs of states are less likely to be involved in MIDs than other pairs of states. Another study in 2000 finds that after both states have become democratic, there is a decreasing probability for MIDs within a year and this decreases almost to zero within five years.

When examining the inter-liberal MIDs in more detail, one study finds that they are less likely to involve third parties, and that the target of the hostility is less likely to reciprocate, if the target reciprocates the response is usually proportional to the provocation, and the disputes are less likely to cause any loss of life. The most common action was ‘Seizure of Material or Personnel.’ Studies find that the probability that disputes between states will be resolved peacefully is positively affected by the degree of democracy exhibited by the lesser democratic state involved in that dispute. Disputes between democratic states are significantly shorter than disputes involving at least one undemocratic state. Democratic states are more likely to be amenable to third party mediation when they are involved in disputes with each other. In international crises that include the threat or use of military force, one study finds that if the parties are democracies, then relative military strength has no effect on who wins. This is different from when nondemocracies are involved. These results are the same also if the conflicting parties are formal allies. Similarly, a study of the behavior of states that joined ongoing militarized disputes reports that power is important only to autocracies: democracies do not seem to base their alignment on the power of the sides in the dispute.

Most of this article discusses research on relations between states. However, there is also evidence that democracies have less internal systematic violence. For instance, one study finds that the most democratic and the most authoritarian states have few civil wars, and intermediate regimes the most. The probability for a civil war is also increased by political change, regardless whether toward greater democracy or greater autocracy. Intermediate regimes continue to be the most prone to civil war, regardless of the time since the political change. In the long run, since intermediate regimes are less stable than autocracies, which in turn are less stable than democracies, durable democracy is the most probable end-point of the process of democratization. Abadie’s (2004) study finds that the most democratic nations have the least terrorism. Harff (2003) finds that genocide and politicide are rare in democracies. Rummel (1997) finds that the more democratic a regime, the less its democide (the murder of any person or people by a government). He finds that democide has killed six times as many people as battles.

Davenport and Armstrong (2004) lists several other studies and states: ‘Repeatedly, democratic political systems have been found to decrease political bans, censorship, torture, disappearances and mass killing, doing so in a linear fashion across diverse measurements, methodologies, time periods, countries, and contexts.’ It concludes: ‘Across measures and methodological techniques, it is found that below a certain level, democracy has no impact on human rights violations, but above this level democracy influences repression in a negative and roughly linear manner.’ Davenport and Armstrong (2003) states that thirty years worth of statistical research has revealed that only two variables decrease human rights violations: political democracy and economic development.

These theories have traditionally been categorized into two groups: explanations that focus on democratic norms and explanations that focus on democratic political structures. Note that they usually are meant to be explanations for little violence between democracies, not for a low level of internal violence in democracies. Several of these mechanisms may also apply to countries of similar systems. The book ‘Never at War’ finds evidence for an oligarchic peace. One example is the Polish-Lithuanian Commonwealth, in which the Sejm resisted and vetoed most royal proposals for war. One example from the first group (democratic norms) is that liberal democratic culture may make the leaders accustomed to negotiation and compromise. Another is that a belief in human rights may make people in democracies reluctant to go to war, especially against other democracies. The decline in colonialism, also by democracies, may be related to a change in perception of non-European peoples and their rights.

Bruce Russett also argues that the democratic culture affects the way leaders resolve conflicts. In addition, he holds that a social norm emerged toward the end of the nineteenth century; that democracies should not fight each other, which strengthened when the democratic culture and the degree of democracy increased, for example by widening the franchise. Increasing democratic stability allowed partners in foreign affairs to perceive a nation as reliable democratic. The alliances between democracies during the two World Wars and the Cold War also strengthened the norms. He sees less effective traces of this norm in Greek antiquity. Austrian philosopher Hans Köchler (1995) relates the question of transnational democracy to empowering the individual citizen by involving him, through procedures of direct democracy, in a country’s international affairs, and he calls for the restructuring of the United Nations according to democratic norms. He refers in particular to the Swiss practice of participatory democracy.

Mousseau argues that it is market-oriented development that creates the norms and values that explain both democracy and the peace. In less developed countries individuals often depend on social networks that impose conformity to in-group norms and beliefs, and loyalty to group leaders. When jobs are plentiful on the market, in contrast, as in market-oriented developed countries, individuals depend on a strong state that enforces contracts equally. Cognitive routines emerge of abiding by state law rather than group leaders, and, as in contracts, tolerating differences among individuals. Voters in marketplace democracies thus accept only impartial ‘liberal’ governments, and constrain leaders to pursue their interests in securing equal access to global markets and in resisting those who distort such access with force. Marketplace democracies thus share common foreign policy interests in the supremacy—and predictability—of international law over brute power politics, and equal and open global trade over closed trade and imperial preferences. When disputes do originate between marketplace democracies, they are less likely than others to escalate to violence because both states, even the stronger one, perceive greater long-term interests in the supremacy of law over power politics.

Braumoeller (1997) argues that liberal norms of conflict resolution vary because liberalism takes many forms. By examining survey results from the newly independent states of the former Soviet Union, the author demonstrates that liberalism in that region bears a stronger resemblance to 19th-century liberal nationalism than to the sort of universalist, Wilsonian liberalism described by democratic peace theorists, and that, as a result, liberals in the region are more, not less, aggressive than non-liberals.

The case for institutional constraints in government goes back to Kant (1795), who wrote: ‘[I]f the consent of the citizens is required in order to decide that war should be declared (and in this constitution it cannot but be the case), nothing is more natural than that they would be very cautious in commencing such a poor game, decreeing for themselves all the calamities of war. Among the latter would be: having to fight, having to pay the costs of war from their own resources, having painfully to repair the devastation war leaves behind, and, to fill up the measure of evils, load themselves with a heavy national debt that would embitter peace itself and that can never be liquidated on account of constant wars in the future’

Democracy thus gives influence to those most likely to be killed or wounded in wars, and their relatives and friends (and to those who pay the bulk of the war taxes). This monadic theory must, however, explain why democracies do attack non-democratic states. One explanation is that these democracies were threatened or otherwise were provoked by the non-democratic states. Doyle argued that the absence of a monadic peace is only to be expected: the same ideologies that cause liberal states to be at peace with each other inspire idealistic wars with the illiberal, whether to defend oppressed foreign minorities or avenge countrymen settled abroad. Doyle also notes liberal states do conduct covert operations against each other; the covert nature of the operation, however, prevents the publicity otherwise characteristic of a free state from applying to the question

Studies show that democratic states are more likely than autocratic states to win wars. One explanation is that democracies, for internal political and economic reasons, have greater resources. This might mean that democratic leaders are unlikely to select other democratic states as targets because they perceive them to be particularly formidable opponents. One study finds that interstate wars have important impacts on the fate of political regimes, and that the probability that a political leader will fall from power in the wake of a lost war is particularly high in democratic states.

Several studies have argued that liberal leaders face institutionalized constraints that impede their capacity to mobilize the state’s resources for war without the consent of a broad spectrum of interests. Survey results that compare the attitudes of citizens and elites in the Soviet successor states are consistent with this argument. Moreover, these constraints are readily apparent to other states and cannot be manipulated by leaders. Thus, democracies send credible signals to other states of an aversion to using force. These signals allow democratic states to avoid conflicts with one another, but they may attract aggression from nondemocratic states. Democracies may be pressured to respond to such aggression—perhaps even preemptively—through the use of force. Also, studies have argued that when democratic leaders do choose to escalate international crises, their threats are taken as highly credible, since there must be a relatively large public opinion for these actions. In disputes between liberal states, the credibility of their bargaining signals allows them to negotiate a peaceful settlement before mobilization.

An explanation based on game theory similar to the last two above is that the participation of the public and the open debate send clear and reliable information regarding the intentions of democracies to other states. In contrast, it is difficult to know the intentions of nondemocratic leaders, what effect concessions will have, and if promises will be kept. Thus there will be mistrust and unwillingness to make concessions if at least one of the parties in a dispute is a nondemocracy. The risk factors for certain types of state have, however, changed since Kant’s time. In the quote above, Kant points to the lack of popular support for war – first that the populace will directly or indirectly suffer in the event of war – as a reason why republics will not tend to go to war. The number of American troops killed or maimed versus the number of Iraqi soldiers and civilians maimed and killed in the American-Iraqi conflict is indicative. This may explain the relatively great willingness of democratic states to attack weak opponents: the Iraq war was, initially at least, highly popular in the United States. The case of the Vietnam War might, nonetheless, indicate a tipping point where publics may no longer accept continuing attrition of their soldiers (even while remaining relatively indifferent to the much higher loss of life on the part of the populations attacked).

There are several logically distinguishable classes of criticism to democratic oeace theory. Note that they usually apply to no wars or few MIDs between democracies, not to little systematic violence in established democracies. Only one study (Schwartz & Skinner 2002) appears to have argued that there have been as many wars between democracies as one would expect between any other couple of states. However, its authors include wars between young and dubious democracies, and very small wars. Others state that, although there may be some evidence for democratic peace, the data sample or the time span may be too small to assess any definitive conclusions. For example, Gowa finds evidence for democratic peace to be insignificant before 1939, because of the too small number of democracies, and offers an alternate explanation for the following period. Gowa’s use of statistics has been criticized, with several other studies and reviews finding different or opposing results. However, this can be seen as the longest-lasting criticism to the theory.

Some authors criticize the definition of democracy by arguing that states continually reinterpret other states’ regime types as a consequence of their own objective interests and motives, such as economic and security concerns. For example, one study reports that Germany was considered a democratic state by Western opinion leaders at the end of the 19th century; yet in the years preceding World War I, when its relations with the United States, France and Britain started deteriorating, Germany was gradually reinterpreted as an autocratic state, in absence of any actual regime change. Shimmin moves a similar criticism regarding the western perception of Milosevic’s Serbia between 1989 and 1999. Rummel replies to this criticism by stating that, in general, studies on democratic peace do not focus on other countries’ perceptions of democracy; and in the specific case of Serbia, by arguing that the limited credit accorded by western democracies to Milosevic in the early ’90s did not amount to a recognition of democracy, but only to the perception that possible alternative leaders could be even worse.

Some democratic peace researchers have been criticized for post hoc reclassifying some specific conflicts as non-wars or political systems as non-democracies without checking and correcting the whole data set used similarly. Supporters and opponents of democratic peace theory agree that this is bad use of statistics, even if a plausible case can be made for the correction. A military affairs columnist for ‘Asia Times’ summarized the above criticism in a journalist’s fashion describing the theory as subject to the no true Scotsman problem: exceptions are explained away as not being between ‘real’ democracies or ‘real’ wars.

Some democratic peace researchers require that the executive result from a substantively contested election. This may be a restrictive definition: For example, the National Archives of the United States notes that ‘For all intents and purposes, George Washington was unopposed for election as President, both in 1789 and 1792.’ (Under the original provisions for the Electoral College, there was no distinction between votes for President and Vice-President: each elector was required to vote for two distinct candidates, with the runner-up to be Vice-President. Every elector cast one of his votes for Washington, John Adams received a majority of the other votes; there were several other candidates: so the election for Vice President was contested.) Sometimes the datasets used have also been criticized. For example, some authors have criticized the ‘Correlates of War’ data for not including civilian deaths in the battle deaths count, especially in civil wars. Weeks and Cohen (2006) argue that most fishing disputes, which include no deaths and generally very limited threats of violence, should be excluded even from the list of military disputes.

Some researchers, while accepting the empirical findings of democratic peace, have looked for alternate explanations other than simply the direct claim that democracy causes peace. One general criticism motivating research of different explanations is that actually the theory cannot claim that ‘democracy causes peace,’ because the evidence for democracies being, in general, more peaceful is very slight or non existent; it only can support the claim that ‘joint democracy causes peace.’ According to Rosato (2003), this casts doubts on whether democracy is actually the cause because, if so, a monadic effect would be expected.

Perhaps the simplest explanation to such perceived anomaly (but not the one the Rosato prefers) is that democracies are not peaceful to each other because they are democratic, but rather because they are similar. This line of thought started with several independent observations of an ‘Autocratic Peace’ effect, a reduced probability of war (obviously no author claims its absence) between states which are both non-democratic, or both highly so. This has led to the hypothesis that democratic peace emerges as a particular case when analyzing a subset of states which are, in fact, similar. Or, that similarity in general does not solely affect the probability of war, but only coherence of strong political regimes such as full democracies and stark autocracies.

Autocratic peace and the explanation based on political similarity is a relatively recent development, and opinions about its value are varied. Henderson (2002) builds a model considering political similarity, geographic distance and economic interdependence as its main variables, and concludes that democratic peace is a statistical artifact which disappears when the above variables are taken into account. Werner (2000) finds a conflict reducing effect from political similarity in general, but with democratic dyads being particularly peaceful, and noting some differences in behavior between democratic and autocratic dyads with respect to alliances and power evaluation. Beck, King and Zeng (2004) use neural networks to show two distinct low probability zones, corresponding to high democracy and high autocracy. Petersen (2004) uses a different statistical model and finds that autocratic peace is not statistically significant, and that the effect attributed to similarity is mostly driven by the pacifying effect of joint democracy.

Ray (2005) similarly disputes the weight of the argument on logical grounds, claiming that statistical analysis on ‘political similarity’ uses a main variable which is an extension of ‘joint democracy’ by linguistic redefinition, and so it is expected that the war reducing effects are carried on in the new analysis. Bennett (2006) builds a direct statistical model based on a triadic classification of states into ‘democratic,’ ‘autocratic’ and ‘mixed.’ He finds that autocratic dyads have a 35% reduced chance of going into any type of armed conflict with respect to a reference mixed dyad. Democratic dyads have a 55% reduced chance. This effect gets stronger when looking at more severe conflicts; for wars (more than 1000 battle deaths), he estimates democratic dyads to have an 82% lower risk than autocratic dyads. He concludes that autocratic peace exists, but democratic peace is clearly stronger. However, he finds no relevant pacifying effect of political similarity, except at the extremes of the scale.

To summarize a rather complex picture, there are no less than four possible stances on the value of this criticism: Political similarity, plus some complementary variables, explains everything. Democratic peace is a statistical artifact. Henderson subscribes to this view. Political similarity has a pacifying effect, but democracy makes it stronger. Werner would probably subscribe to this view. Political similarity in general has little or no effect, except at the extremes of the democracy-autocracy scale: a democratic peace and an autocratic peace exist separately, with the first one being stronger, and may have different explanations. Bennett holds this view, and Kinsella mentions this as a possibility. Political similarity has little or no effect and there is no evidence for autocratic peace. Petersen and Ray are among defendants of this view.

A majority of researchers on the determinants of democracy agree that economic development is a primary factor which allows the formation of a stable and healthy democracy. Thus, some researchers have argued that economic development also plays a factor in the establishment of peace. Mousseau argues that a culture of contracting in advanced market-oriented economies may cause both democracy and peace. These studies indicate that democracy, alone, is an unlikely cause of the democratic peace. A low level of market-oriented economic development may hinder development of liberal institutions and values. Hegre (2000) and Souva (2003) confirmed these expectations. Mousseau (2005) finds that democracy is a significant factor only when both democracies have levels of economic development well above the global median. In fact, the poorest 21% of the democracies studied, and the poorest 4–5% of current democracies, are significantly more likely than other kinds of countries to fight each other. Mousseau, Hegre & Oneal (2003) confirm that if at least one of the democracies involved has a very low level of economic development, democracy is ineffective in preventing war; however, they find that when also controlling for trade, 91% of all the democratic pairs had high enough development for the pacifying effect of democracy to be important during the 1885–1992 period and all in 1992.

Both World Wars were fought between countries which can be considered economically developed. Mousseau argues that both Germany and Japan – like the USSR during the Cold War and Saudi Arabia today – had state-managed economies and thus lacked his market norms. Hegre (2003) finds that democracy is correlated with civil peace only for developed countries, and for countries with high levels of literacy. Conversely, the risk of civil war decreases with development only for democratic countries. Gartzke (2005) argues that economic freedom (a quite different concept from Mousseau’s market norms) or financial dependence explains the developed democratic peace, and these countries may be weak on these dimensions too.

Several studies find that democracy, more trade causing greater economic interdependence, and membership in more intergovernmental organizations reduce the risk of war. This is often called the Kantian peace theory since it is similar to Kant’s earlier theory about a perpetual peace; it is often also called ‘liberal peace’ theory, especially when one focuses on the effects of trade and democracy. (The theory that free trade can cause peace is quite old and referred to as Cobdenism.) Many researchers agree that these variables positively affect each other but each has a separate pacifying effect. For example, in countries exchanging a substantial amount of trade, economic interest groups may exist that oppose a reciprocal disruptive war, but in democracy such groups may have more power, and the political leaders be more likely to accept their requests. None of the authors listed argues that free trade alone causes peace. Even so, the issue of whether free trade or democracy is more important in maintaining peace may have potentially significant practical consequences, for example on evaluating the effectiveness of applying economic sanctions and restrictions to autocratic countries.

It was Michael Doyle (1983, 1997) who reintroduced Kant’s three articles into democratic peace theory. He argued that a pacific union of liberal states has been growing for the past two centuries. He denies that a pair of states will be peaceful simply because they are both liberal democracies; if that were enough, liberal states would not be aggressive towards weak non-liberal states (as the history of American relations with Mexico shows they are). Rather, liberal democracy is a necessary condition for international organization and hospitality (which are Kant’s other two articles)—and all three are sufficient to produce peace. Other Kantians have not repeated Doyle’s argument that all three in the triad must be present, instead stating that all three reduce the risk of war.

Many studies supporting the theory have controlled for many possible alternative causes of the peace. Examples of factors controlled for are geographic distance, geographic contiguity, power status, alliance ties, militarization, economic wealth, and economic growth, power ratio, and political stability. These studies have often found very different results depending on methodology and included variables, which has caused criticism. It should be noted that DPT does not state democracy is the only thing affecting the risk of military conflict. Many of the mentioned studies have found that other factors are also important. However, a common thread in most results is an emphasis on the relationship between democracy and peace.

Several studies have also controlled for the possibility of reverse causality from peace to democracy. For example, one study (Reuveny & Li 2003) supports the theory of simultaneous causation, finding that dyads involved in wars are likely to experience a decrease in joint democracy, which in turn increases the probability of further war. So they argue that disputes between democratizing or democratic states should be resolved externally at a very early stage, in order to stabilize the system. Another study (Reiter 2001) finds that peace does not spread democracy, but spreading democracy is likely to spread peace. A different kind of reverse causation lies in the suggestion that impending war could destroy or decrease democracy, because the preparation for war might include political restrictions, which may be the cause for the findings of democratic peace. However, this hypothesis has been statistically tested in a study (Mousseau & Shi 1999) whose authors find, depending on the definition of the pre-war period, no such effect or a very slight one. So, they find this explanation unlikely. Note also that this explanation would predict a monadic effect, although weaker than the dyadic one.

Weart (1998) argues that the peacefulness appears and disappears rapidly when democracy appears and disappears. This in his view makes it unlikely that variables that change more slowly are the explanation. Weart, however, has been criticized for not offering any quantitative analysis supporting his claims (Ray, 2000). Wars tend very strongly to be between neighboring states. Gleditsch (1995) showed that the average distance between democracies is about 8000 miles, the same as the average distance between all states. He believes that the effect of distance in preventing war, modified by the democratic peace, explains the incidence of war as fully as it can be explained.

Supporters of realism in international relations in general argue that not democracy or its absence, but considerations and evaluations of power, cause peace or war. Specifically, many realist critics claim that the effect ascribed to democratic, or liberal, peace, is in fact due to alliance ties between democratic states which in turn are caused, one way or another, by realist factors. For example, Farber and Gowa (1995) find evidence for peace between democracies to be statistically significant only in the period from 1945 on, and consider such peace an artifact of the Cold War, when the threat from the communist states forced democracies to ally with one another. Mearsheimer (1990) offers a similar analysis of the Anglo-American peace before 1945, caused by the German threat. Spiro (1994) finds several instances of wars between democracies, arguing that evidence in favor of the theory might be not so vast as other authors report, and claims that the remaining evidence consists of peace between allied states with shared objectives. He acknowledges that democratic states might have a somewhat greater tendency to ally with one another, and regards this as the only real effect of democratic peace.

Rosato (2003) argues that most of the significant evidence for democratic peace has been observed after World War II; and that it has happened within a broad alliance, which can be identified with NATO and its satellite nations, imposed and maintained by American dominance (Pax Americana). One of the main points in Rosato’s argument is that, although never engaged in open war with another liberal democracy during the Cold War, the United States intervened openly or covertly in the political affairs of democratic states several times, for example in the Chilean coup of 1973, the 1953 coup in Iran, and 1954 coup in Guatemala; in Rosato’s view, these interventions show the United States’ determination to maintain an ‘imperial peace.’

The most direct counter arguments to such criticisms have been studies finding peace between democracies to be significant even when controlling for ‘common interests’ as reflected in alliance ties. Regarding specific issues, Ray (1998) objects that explanations based on the Cold War should predict that the Communist bloc would be at peace within itself also, but exceptions include the Soviet Invasion of Afghanistan, the Cambodian-Vietnamese War, and the Sino-Vietnamese War. Ray also argues that the external threat did not prevent conflicts in the Western bloc when at least one of the involved states was a nondemocracy, such as the Turkish Invasion of Cyprus (against Greek Junta supported Cypriot Greeks), the Falklands War, and the Football War. Also, one study notes that the explanation ‘goes increasingly stale as the post-Cold War world accumulates an increasing number of peaceful dyad-years between democracies.’

Rosato (2003) criticizes most explanations to how democracy might cause peace. Arguments based on normative constraints, he argues, are not consistent with the fact that democracies do go to war no less than other states, thus violating norms preventing war; for the same reason he refutes arguments based on the importance of public opinion. Regarding explanations based on greater accountability of leaders, he finds that historically autocratic leaders have been removed or punished more often than democratic leaders when they get involved in costly wars. Finally, he also criticizes the arguments that democracies treat each other with trust and respect even during crises; and that democracy might be slow to mobilize its composite and diverse groups and opinions, hindering the start of a war, drawing support from other authors. Another realist, Layne (1994) analyzes the crises and brinkmanship that took place between non-allied democratic great powers, during the relatively brief period when such existed. He finds no evidence either of institutional or cultural constraints against war; indeed, there was popular sentiment in favor of war on both sides. Instead, in all cases, one side concluded that it could not afford to risk that war at that time, and made the necessary concessions.

A different kind of realist criticism is centered around the role of nuclear weapons in maintaining peace. In realist terms, this means that, in the case of disputes between nuclear powers, respective evaluation of power might be irrelevant because of Mutual assured destruction preventing both sides from foreseeing what could be reasonably called a ‘victory.’ The 1999 Kargil War between India and Pakistan has been cited as a counterexample to this argument. Immanuel Wallerstein has argued that it is the global capitalist system that creates shared interests among the dominant parties, thus inhibiting potentially harmful belligerence. Negri and Hardt take a similar stance, arguing that the intertwined network of interests in the global capitalism leads to the decline of individual nation states, and the rise of a global Empire which has no outside, and no external enemies. As a result, they write, ‘The era of imperialist, interimperialist, and anti-imperialist wars is over. (…) we have entered the era of minor and internal conflicts. Every imperial war is a civil war, a police action.’

Democratic peace researchers do in general not count as wars conflicts which do not kill a thousand on the battlefield; thus they exclude for example the bloodless Cod Wars. However, as noted earlier, research has also found a peacefulness between democracies when looking at lesser conflicts. Democracies were involved in more colonial and imperialistic wars than other states during the 1816–1945 period. On the other hand, this relation disappears if controlling for factors like power and number of colonies. Liberal democracies have less of these wars than other states after 1945. This might be related to changes in the perception of non-European peoples, as embodied in the Universal Declaration of Human Rights.

Related to this is the human rights violations committed against native people, sometimes by liberal democracies. One response is that many of the worst crimes were committed by nondemocracies, like in the European colonies before the nineteenth century, in King Leopold II of Belgium’s privately owned Congo Free State, and in Joseph Stalin’s Soviet Union. The United Kingdom abolished slavery in British territory in 1833, immediately after the Reform Act 1832 had significantly enlarged the franchise. (Of course, the abolition of the slave trade had been enacted in 1807; and many DPT supporters would deny that the UK was a liberal democracy in 1833 when examining interstate wars.)

Hermann and Kegley (1995) argue that interventions between democracies are more likely to happen than projected by an expected model. They further argue (1996) that democracies are more likely to intervene in other liberal states than against countries that are non-democracies. Finally, they argue that these interventions between democracies have been increasing over time and that the world can expect more of these interventions in the future. Rummel argues that the continuing increase in democracy worldwide will soon lead to an end to wars and democide, possibly around or even before the middle of this century. The fall of Communism and the increase in the number of democratic states were accompanied by a sudden and dramatic decline in total warfare, interstate wars, ethnic wars, revolutionary wars, and the number of refugees and displaced persons. One report claims that the two main causes of this decline in warfare are the end of the Cold War itself and decolonization; but also claims that the three Kantian factors have contributed materially.

The capitalist peace, or capitalist peace theory, posits that according to a given criteria for economic development (capitalism), developed economies have not engaged in war with each other, and rarely enter into low-level disputes. These theories have been proposed as an explanation for the democratic peace by accounting for both democracy and the peace among democratic nations. The exact nature of the causality depends upon both the proposed variable and the measure of the indicator for the concept used. In Thomas L. Friedman’s 1999 book ‘The Lexus and the Olive Tree,’ the following observation was presented: ‘No two countries that both had McDonald’s had fought a war against each other since each got its McDonald’s.’ He supported that observation, as a theory, by stating that when a country has reached an economic development where it has a middle class strong enough to support a McDonalds network, it would become a ‘McDonald’s country,’ and will not be interested in fighting wars anymore. Shortly after the book was published, NATO bombed Yugoslovia. On the first day of the bombing, McDonald’s restaurants in Belgrade were demolished by angry protesters and were rebuilt only after the bombing ended. In the 2000 edition of the book, Friedman argued that this exception proved the rule: the war ended quickly, he argued, partly because the Serbian population did not want to lose their place in a global system ‘symbolized by McDonald’s.’

In 1999, India and Pakistan fought a war over Kashmir, known as the Kargil War. Both countries have (and continue to have) McDonald’s restaurants. Although the war was not fought in all possible theaters (such as Rajasthan and Punjab borders), both countries moblized their military all along their common borders and both countries made threats involving their nuclear capabilities. In 2005, Friedman said that he framed this theory in terms of McDonald’s Golden Arches ‘with tongue slightly in cheek.’ In his 2005 book ‘The World is Flat’ he offered an updated theory he labelled the Dell Theory of Conflict Prevention. Friedman’s point is that due to globalization, countries that have made strong economic ties with one another have too much to lose to ever go to war with one another. Regardless of whether the statement is true, the conclusions to be drawn are unclear. The global expansion of McDonald’s restaurants is a relatively recent phenomenon when put into the context of the history of warfare, and, with a few notable exceptions, has proceeded into relatively stable markets.

Some fear that the democratic peace theory may be used to justify wars against nondemocracies in order to bring lasting peace, in a democratic crusade. Woodrow Wilson in 1917 asked Congress to declare war against Imperial Germany, citing Germany’s sinking of American ships due to unrestricted submarine warfare and the Zimmermann telegram, but also stating that ‘A steadfast concert for peace can never be maintained except by a partnership of democratic nations’ and ‘The world must be made safe for democracy.’ R. J. Rummel is a notable proponent of war for the purpose of spreading democracy, based on this theory.

Some point out that the democratic peace theory has been used to justify the 2003 Iraq War, others argue that this justification was used only after the war had already started (Russett 2005). Furthermore, Weede (2004) has argued that the justification is extremely weak, because forcibly democratizing a country completely surrounded by non-democracies, most of which are full autocracies, as Iraq was, is at least as likely to increase the risk of war as it is to decrease it (some studies show that dyads formed by one democracy and one autocracy are the most warlike, and several find that the risk of war is greatly increased in democratizing countries surrounded by nondemocracies). According to Weede, if the United States and its allies wanted to adopt a rationale strategy of forced democratization based on democratic peace, which he still does not recommend, it would be best to start intervening in countries which border with at least one or two stable democracies, and expand gradually.

Also, research shows that attempts to create democracies by using external force has often failed. Gleditsch, Christiansen and Hegre (2004) argue that forced democratization by interventionism may initially have partial success, but often create an unstable democratizing country, which can have dangerous consequences in the long run. Those attempts which had a permanent and stable success, like democratization in Austria, West Germany, and Japan after World War II, mostly involved countries which had an advanced economic and social structure already, and implied a drastic change of the whole political culture. Supporting internal democratic movements and using diplomacy may be far more successful and less costly. Thus, the theory and related research, if they were correctly understood, may actually be an argument against a democratic crusade.

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