What Is the Democratic Peace Theory? Definition and Examples

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The Democratic Peace Theory states that countries with liberal democratic forms of government are less likely to go to war with one another than those with other forms of government. Proponents of the theory draw on the writings of German philosopher Immanuel Kant and, more recently, U.S. President Woodrow Wilson , who in his 1917 World War I message to Congress stated that “The world must be made safe for democracy.” Critics argue that the simple quality of being democratic in nature may not be the main reason for the historic tendency of peace between democracies.

Key Takeaways

Democratic Peace Theory Definition

Dependent on the ideologies of liberalism , such as civil liberties and political freedom, the Democratic Peace Theory holds that democracies are hesitant to go to war with other democratic countries. Proponents cite several reasons for the tendency of democratic states to maintain peace, including:

The Democratic Peace Theory was first articulated by German philosopher Immanuel Kant in his 1795 essay entitled “ Perpetual Peace .” In this work, Kant argues that nations with constitutional republic governments are less likely to go to war because doing so requires the consent of the people—who would actually be fighting the war. While the kings and queens of monarchies can unilaterally declare war with little regard for their subjects’ safety, governments chosen by the people take the decision more seriously.

The United States first promoted the concepts of the Democratic Peace Theory in 1832 by adopting the Monroe Doctrine . In this historic piece of international policy, the U.S. affirmed that it would not tolerate any attempt by European monarchies to colonize any democratic nation in North or South America.

The democratic peace theory does not claim that democratic countries are generally more peaceful than nondemocratic countries. However, the theory’s claim that democratic countries rarely fight each other is widely regarded as true by international relations experts and further supported by history. 

Kant’s “Perpetual Peace” essay remained largely unnoticed until the mid-1980s when the American international-relations scholar Michael Doyle cited it in arguing that the “zone of peace” envisioned by Kant had gradually become reality. After the Cold War, which pitted democratic states against communist states, the democratic peace theory became one of the most studied topics of research in international relations. This research has shown that while wars between non-democracies, or between democracies and non-democracies have been common, wars between democracies have been extremely rare.

Interest in the democratic peace theory has not been limited to the halls of academia. During the 1990s, U.S. President Bill Clinton featured it in many aspects of his administration’s foreign policy of spreading democracy throughout the world. Clinton’s foreign policy asserted that if the formerly autocratic nations of Eastern Europe and the collapsed Soviet Union converted to democracy, the United States and its allies in Europe would no longer need to restrain those countries militarily because democracies do not attack each other.

The democratic peace theory similarly influenced U.S. foreign policy in the Middle East in the aftermath of the September 11, 2001, terrorist attacks. U.S. policymakers believed that a zone of democracy equaled a zone of peace and security that supported President George W. Bush’s strategy of using military force to overthrow Saddam Hussein’s ruthless dictatorship in Iraq. Bush’s administration hoped that the democratization of Iraq would eventually result in the spread of democracy throughout the Middle East.

Democracies and War in the 1900s

Perhaps the strongest evidence supporting the Democratic Peace Theory is the fact that there were no wars between democracies during the 20th century.

As the century began, the recently ended Spanish-American War had seen the United States defeat the monarchy of Spain in a struggle for control of the Spanish colony of Cuba.

In World War I , the U.S. allied with the democratic European empires to defeat the authoritarian and fascist empires of Germany, Austro-Hungary, Turkey, and their allies. This led to World War II and eventually the Cold War of the 1970s, during which the U.S. led a coalition of democratic nations in resisting the spread of authoritarian Soviet communism .

Most recently, in the Gulf War (1990-91), the Iraq War (2003-2011), and the ongoing war in Afghanistan , the United States, along with various democratic nations fought to counter international terrorism by radical jihadist factions of authoritarian Islamist governments. Indeed, after the September 11, 2001, terror attacks , the George W. Bush administration based its use military force to topple Saddam Hussein’s dictatorship in Iraq on the belief that it would bring democracy—thus peace—to the Middle East.

While the claim that democracies rarely fight each other has been widely accepted, there is less agreement on why this so-called democratic peace exists.

Some critics have argued that it was actually the Industrial Revolution that led to peace during the nineteenth and twentieth centuries. The resulting prosperity and economic stability made all of the newly modernized countries—democratic and nondemocratic—much less belligerent toward each other than in preindustrial times. Several factors arising from modernization may have generated a greater aversion to war among industrialized nations than democracy alone. Such factors included higher standards of living, less poverty, full employment, more leisure time, and the spread of consumerism. Modernized countries simply no longer felt the need to dominate each other in order to survive.

Democratic Peace Theory has also been criticized for failing to prove a cause-and-effect relationship between wars and types of government and the ease with which definitions of “democracy” and “war” can be manipulated to prove a non-existent trend. While its authors included very small, even bloodless wars between new and questionable democracies, one 2002 study contends that as many wars have been fought between democracies as might be statistically expected between non-democracies.

Other critics argue that throughout history, it has been the evolution of power, more than democracy or its absence that has determined peace or war. Specifically, they suggest that the effect called “liberal democratic peace” is really due to “realist” factors including military and economic alliances between democratic governments.

Sources and Further Reference

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Democratic Peace Theory by Dan Reiter LAST REVIEWED: 02 May 2019 LAST MODIFIED: 25 October 2012 DOI: 10.1093/obo/9780199756223-0014

Democratic peace is the proposition that democracies are more peaceful in their foreign relations. This idea dates back centuries, at least to Immanuel Kant and other 18th-century Enlightenment thinkers. In recent decades it has constituted a major research agenda, competing with and arguably supplanting other research agendas such as neo-realism. The democratic peace proposition has many possible empirical and theoretical forms. On the empirical side, some propose that democracies are more peaceful in their relations with all other states in the system (“monadic” democratic peace); some propose that democracies are more peaceful only in their relations with other democracies (“dyadic” democratic peace); others argue that the more democracies there are in a region or the international system, the more peaceful the region or international system will be (“systemic” democratic peace); and still others doubt the existence of any significant relationship between democracy and peace. Notably, most although not all empirical research on the democratic peace has employed quantitative methods of analysis. On the theoretical side, there are many different accounts of the relationship between democracy and peace, with most focusing on domestic political institutions, domestic political norms, and constructed identities. The democratic peace proposition is connected to many other propositions linking domestic politics and international relations, including that democracies are more likely to cooperate with each other, that democracies are more likely to win the wars they fight, that escalating military casualties degrade public support for war, that leaders initiate conflict to secure their domestic hold on power (the diversionary hypothesis), that democracies fight shorter wars, that different kinds of democracies experience different kinds of conflict behavior, that different kinds of authoritarian systems experience different kinds of conflict behavior, and others. The democratic peace also overlaps with related ideas such as the liberal peace and the commercial peace.

The democratic peace proposition has been lurking in Western thought for millennia, as Weart 1998 shows, but Kant 1991 provides its first modern formulation. The idea that global democracy would provide a solid foundation for global peace was restated in 1917 by Woodrow Wilson as a justification for American entry into World War I and then as part of his vision for a new world order. Modern political science first observed the dyadic democratic peace—that democracies tend not to fight each other—in the 1970s. The observation enjoyed greater attention in the 1980s in particular in two pathbreaking 1983 essays by Michael Doyle, reprinted in Doyle 2011 . It received fuller theoretical and empirical attention in the 1990s. Fukuyama 1992 , a famous argument that humanity had reached “the end of history,” incorporates the democratic peace proposition. Other scholars sought to develop the theory and push forward more advanced research designs in works such as Russett 1993 ; Ray 1995 ; and Rousseau, et al. 1996 . In the 2000s, proponents of the democratic peace responded to their critics and embedded the democratic peace in a broader Kantian peace ( Russett and Oneal 2001 ).

Doyle, Michael W. Liberal Peace: Selected Essays . New York: Routledge, 2011.

Contains a number of Doyle’s important essays, especially from the 1980s, that lay out the philosophical and theoretical basis of the democratic peace.

Fukuyama, Francis. The End of History and the Last Man . New York: Free Press, 1992.

Presents a Hegelian argument that humanity has at last achieved its penultimate form of political and economic organization, liberal democracy. The definitive intellectual statement that Western values triumphed in the Cold War.

Huth, Paul K., and Todd L. Allee. The Democratic Peace and Territorial Conflict in the Twentieth Century . Cambridge, UK: Cambridge University Press, 2002.

Application of the democratic peace to territorial conflict in the 20th century. Presents a massive new data set on territorial conflicts.

Kant, Immanuel. Kant’s Political Writings . 2d ed. Edited by Hans S. Reiss. Cambridge, UK: Cambridge University Press, 1991.

Central essay is on the “perpetual peace,” which presents Kant’s vision as to how republics can maintain world peace. Originally published in 1796.

Ray, James Lee. Democracy and International Conflict: An Evaluation of the Democratic Peace Proposition . Columbia: University of South Carolina Press, 1995.

Provides an extensive literature review on democratic peace literature up to the early 1990s as well as case studies of the Fashoda Crisis and Spanish-American War.

Rousseau, David L., Christopher Gelpi, Dan Reiter, and Paul K. Huth. “Assessing the Dyadic Nature of the Democratic Peace, 1918–1988.” American Political Science Review 90.3 (1996): 512–533.

DOI: 10.2307/2082606

Important, early empirical test of the democratic peace, presenting important research design advances.Available online by subscription.

Russett, Bruce. Grasping the Democratic Peace: Principles for a Post–Cold War World . Princeton, NJ: Princeton University Press, 1993.

The first book-length treatment of the democratic peace. Lays out the normative and institutional explanations of the democratic peace and presents a variety of different forms of rigorous evidence demonstrating the dyadic democratic peace, including sophisticated analysis of post-1945 conflict behavior.

Russett, Bruce, and John R. Oneal. Triangulating Peace: Democracy, Interdependence, and International Organizations . New York: Norton, 2001.

Embedded the democratic peace in a larger theoretical framework, the Kantian Peace, in which democracy, trade, international organization, and peace all mutually reinforce each other. Presented more sophisticated empirical tests, addressing many 1990s theoretical and empirical critiques. Also see Democratization .

Weart, Spencer R. Never at War: Why Democracies Will Never Fight One Another . New Haven, CT: Yale University Press, 1998.

Summarizes several years of work on democratic peace theory. Presents a narrative rather than statistical empirical tests. One main contribution is the analysis of democratic peace in pre-Napoleonic times, including ancient Greece and medieval Italy. Discusses the phenomena of democratic aggression and imperialism.

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Encyclopedia Britannica

democratic peace

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democratic peace , the proposition that democratic states never (or almost never) wage war on one another.

The concept of democratic peace must be distinguished from the claim that democracies are in general more peaceful than nondemocratic countries. Whereas the latter claim is controversial, the claim that democratic states do not fight each other is widely regarded as true by scholars and practitioners of international relations . Proponents of the democratic peace hark back to the German philosopher Immanuel Kant and, more recently, to U.S. Pres. Woodrow Wilson , who declared in his 1917 war message to Congress that the United States aimed to make the world “safe for democracy.”

In Project for a Perpetual Peace (1795), Kant envisioned the establishment of a zone of peace among states constituted as republics . Although he explicitly equated democracy with despotism, contemporary scholars claim that Kant’s definition of republicanism, which emphasizes the representative nature of republican government, corresponds to our current understanding of liberal democracy . Thus, the terms democratic peace (or liberal peace ) and Kantian peace are today often used interchangeably.

Project for a Perpetual Peace received little notice from students of international relations until, in a series of influential articles published in the mid-1980s, the American international-relations scholar Michael Doyle called attention to Kant’s work and argued that the zone of peace envisioned by Kant has gradually become reality. Subsequently, and especially after the end of the Cold War , the democratic peace became one of the most-popular subjects of research in international relations. Scores of studies were devoted to it, many of which employed quantitative methods to demonstrate that the democratic peace is a historical fact. What that research has shown is not that wars between nondemocracies, or between democracies and nondemocracies, have been frequent; instead, it has demonstrated that, although interstate war is a rare event in general, wars between democracies have been even rarer.

Although a number of critics have questioned the veracity of the proposition, the claim that democracies do not fight each other continues to be widely accepted in the international relations discipline . There is less agreement, however, on why the democratic peace exists. Two major competing (if not mutually exclusive) explanations have been elaborated. While some argue that democracies are more peaceful to one another because of a shared culture , others consider the main factor to be structural (or institutional). Proponents of the first view argue that the political culture of democratic societies is pervaded by the norm that disputes are to be settled by peaceful means. Democratic citizenries, the argument goes, apply that norm to their relations with other democratic societies; hence, when two democracies are locked in a dispute, their leaders expect each other to shun violent means of resolving the dispute. Proponents of the second explanation argue that the political institutions in democracies matter more than the norms harboured by their citizens. The separation of powers and the checks and balances characteristic of democratic political systems constrain the ability of elected leaders to move their countries rashly toward war. Thus, when a conflict arises between two democratic countries, their leaders need not fear a surprise attack; the inherently slow process of national-security decision making on both sides allows ample time for diplomats to resolve the conflict peacefully.

In the debate over international relations theory, the democratic peace is identified with the liberal perspective, and it is closely associated with two other liberal claims about world politics: that international peace is promoted by (a) economic interdependence between states and (b) international institutions. The major rival of international liberal theory is realism , which contends that the foreign policy behaviour of states is shaped primarily by the anarchic structure of the international system—that is, by the absence of a supranational authority capable of effectively providing for the security of individual states. For realists, so long as the international system is anarchic, violence will remain latent, if not always overt, in world politics regardless of the internal characteristics of individual states (e.g., their regime type). Thus, to the extent that a perpetual state of peace indeed prevails among liberal democracies, its emergence contradicts realist expectations and undermines the position of realism as the leading theory of international relations.

The popularity of the democratic peace idea has not been confined to the academy. The foreign policy rhetoric of U.S. Pres. Bill Clinton during the 1990s featured many appeals to this thesis. Spreading democracy throughout the globe was a principal aim of his foreign policy, and administration officials used the democratic peace idea to justify that policy. If the formerly autocratic nations of eastern Europe and the former Soviet Union democratized successfully, the argument went, the United States and its western European allies would no longer need to contain these nations militarily, because democracies do not fight each other.

The democratic peace was also embraced by the neoconservative thinkers and officials who shaped U.S. foreign policy in the Middle East in the aftermath of the September 11, 2001, attacks . The belief that a zone of democracy equaled a zone of peace and security buttressed the desire of the George W. Bush administration to use force to topple Saddam Hussein ’s dictatorship in Iraq and its expectation that the democratization of that country would result in the spread of democracy throughout the Middle East.


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