war

Introduction
Evolution of theories of war
The causes of war
- Biological theories
  - Ethology
  - Psychology
- Social theories
  - Liberal analyses
  - Socialist analyses
  - Nationalism
  - Special-interest groups
The control of war
- Diplomacy
- Regional integration
- International law
- The United Nations
  - Peaceful settlement of disputes
  - Collective security
  - Disarmament
  - Limiting conflict
- World government

References & Edit History Quick Facts & Related Topics

Images & Videos

Painting of the Battle of Waterloo showing British infantry and cavalry, some with a Union Jack flag, resisting a French cavalry charge amid smoke and chaos on the battlefield.

World War I soldiers walk through muddy, debris-strewn ruins with the damaged Cloth Hall of Ypres, Belgium, standing in the background under a cloudy sky.

Learn about the social behavior of bonobos

Portrait of Benedict de Spinoza, 17th-century Dutch-Jewish philosopher, with shoulder-length dark hair, white collar, and black robe, set against a dark background.

At a Glance

war summary

Quizzes

Civil War era cannon overlooks Kennesaw Mountain National Battle. (military, artillery, American history)

Pick Your Battles Quiz

Louis IX of France (St. Louis), stained glass window of Louis IX during the Crusades. (Unknown location.)

World Wars

Union Soldiers. Bottom half of the memorial honoring American Civil War General and U.S. President Ulysses S. Grant at the base of Capitol Hill, Washington, DC. Photo: 2010 Memorial Day

History of Warfare

A soldier standing guard in a Washington, D.C. street with the ruins of buildings that were destroyed during the riots that followed the assassination of Martin Luther King, Jr., April 8, 1968.

By All Military Meanings Necessary: Vocab Quiz

Related Questions

How are civil wars different from riots and terrorist violence?
How can ethnic identity and ideology both contribute to the same civil war?
How can the UN Security Council authorize the use of military force?
How can war reduce living standards by diverting resources from civilian needs?
How did Christian ideas influence early European rules about conduct in war?
How did the attempts to create Biafra and Bangladesh show the role of nationalism in war?
How did the principle of national self-determination shape political boundaries after World War I?
How does the Geneva Convention on prisoners of war require captors to treat prisoners?
How does the UN Charter seek to limit the use of armed force between states?
How is a civil war different from a war between two countries?
What did the Geneva Gas Protocol of 1925 ban in warfare?
What human costs of war go beyond deaths on the battlefield?
What ideas about war did Hugo Grotius explore in On the Law of War and Peace?
What is the opportunity cost of spending resources on a war?
Which weapons were prohibited by the Declaration of St. Petersburg of 1868?
Why are humanitarian military interventions controversial under international law?
Why are international laws against war difficult to enforce?
Why are poison and poisoned weapons prohibited under the Hague Convention of 1907?
Why are preemptive military strikes controversial under international law?
Why can national minorities seeking independence create international conflict?
Why can nationalism make compromise and accepting defeat more difficult during war?
Why can nationalist movements lead to wars between states or groups?
Why did chivalry fail to protect ordinary soldiers and civilians in earlier wars?
Why did following superior orders not completely excuse defendants at the Nürnberg Trials?
Why do the laws of war give equal protections to fighters on both sides of a conflict?
Why does international law prohibit weapons designed to cause unnecessary suffering?
Why does the Hague Convention of 1907 say that the right to injure an enemy is not unlimited?
Why is the legality of using nuclear weapons under international law debated?
Why must self-defense be necessary and proportionate under international law?
Why were international war-crimes tribunals established for Yugoslavia and Rwanda?
What are the differences between domestic and international terrorism?
What are the types of terrorism?
What is the U.S. Navy’s “gender neutral” submarine?
Which country had the most nuclear weapons?
How does a nuclear weapon work?
What is the concept of just war?
What are the origins of just war theory?
How was trench warfare used in World War I?

History Wars, Battles & Armed Conflicts

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External Websites

Social Sciences LibreTexts - War in International Relations
Stanford Encyclopedia of Philosophy - War
National Center for Biotechnology Information - PubMed Central - Mental health consequences of war: a brief review of research findings
World History Encyclopedia - Warfare
Internet Encyclopedia of Philosophy - The Philosophy of War

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

war - Children's Encyclopedia (Ages 8-11)
warfare - Student Encyclopedia (Ages 11 and up)

Korean War United Nations forces fighting to recapture Seoul from communist invaders, September 1950.

war

conflict

Also known as: warfare

Written by

Joseph Frankel

Professor of Politics, University of Southampton, England, 1963–78. Author of The Making of Foreign Policy and others.

Joseph Frankel

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Nov. 11, 2026 •History

war, in the popular sense, a conflict between political groups involving hostilities of considerable duration and magnitude. In the usage of social science, certain qualifications are added. Sociologists usually apply the term to such conflicts only if they are initiated and conducted in accordance with socially recognized forms. They treat war as an institution recognized in custom or in law. Military writers usually confine the term to hostilities in which the contending groups are sufficiently...

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