What Is the Democratic Peace Theory? Definition and Examples

Multilateral meeting, United Nations General Assembly
US President Donald Trump (C) attends a multilateral meeting on Venezuela in New York, September 25, 2019, on the sidelines of the United Nations General Assembly.

 SAUL LOEB / Getty Images

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

  • The Democratic Peace Theory holds that democratic countries are less likely to go to war with one another than non-democratic countries.
  • The theory evolved from the writings of German philosopher Immanuel Kant and the adoption of the 1832 Monroe Doctrine by the United States.
  • The theory is based on the fact that declaring war in democratic countries requires citizen support and legislative approval.
  • Critics of the theory argue that merely being democratic may not be the primary reason for peace between democracies.

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 citizens of democracies usually have some say over legislative decisions to declare war.
  • In democracies, the voting public holds their elected leaders responsible for human and financial war losses.
  • When held publicly accountable, government leaders are likely to create diplomatic institutions for resolving international tensions.
  • Democracies rarely view countries with similar policies and form of government as hostile.
  • Usually possessing more wealth that other states, democracies avoid war to preserve their resources.

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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Longley, Robert. "What Is the Democratic Peace Theory? Definition and Examples." ThoughtCo, Jan. 2, 2022, thoughtco.com/democratic-peace-theory-4769410. Longley, Robert. (2022, January 2). What Is the Democratic Peace Theory? Definition and Examples. Retrieved from https://www.thoughtco.com/democratic-peace-theory-4769410 Longley, Robert. "What Is the Democratic Peace Theory? Definition and Examples." ThoughtCo. https://www.thoughtco.com/democratic-peace-theory-4769410 (accessed May 30, 2023).