War has been far too common in human history and thus is the central problem of international relations. Many political scientists and foreign policymakers view war as the continuation of politics: When diplomacy fails, some states decide to use force. Others see war as the result of a breakdown of the modern international system because so many of the rules of international institutions were designed to reduce conflict among states.

Causes of War

Political scientists have long debated the causes of war. These scholars have come up with the following list:

  • Human nature: Humans are naturally violent and aggressive, making war inevitable.
  • Regime types: Some regimes are more prone to waging war than others.

Example: There has been extensive research on whether democracies are less likely to start wars than other regimes. Overall, it appears that democracies are less likely to fight other democracies, a phenomenon scholars refer to as the democratic peace. Democracies are, however, just as likely as other types of regimes to fight nondemocracies.

  • Ideology: Some political beliefs favor war more than others. Some scholars blame fascism, for example, for World War II.
  • Religion: Religious belief has driven many states to war, either to spread the faith or to eradicate heretics.

Example: During the early modern era, nearly every European country experienced numerous wars of religion as the Catholics sought to destroy the Protestants. The wars of religion culminated in the Thirty Years’ War, which stretched from Spain and France to the eastern stretches of Germany during the seventeenth century. It was a brutal and horrific war, and the Catholics’ failure to win the war marked the end of the major religious wars in Europe.

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