Military conflict took place during every year of the 20th Century. There were only short periods of time that the world was free of war. The total number of deaths caused by war during the 20th Century has been estimated at 187 million and is probably higher.

The following list includes some of the wars fought by the armed forces of the United Kingdom, the British Empire and the British Commonwealth since 1900.

The Second Anglo-Boer War, 18991902

The First World War, 1914–1918

The Russian Civil War, 1917–1922

The Irish War of Independence, 19191921

The Irish Civil War, 1922–1923

The Second World War, 19391945

The Korean War, 1950–1953

The Kenya Emergency, 1952–1960

The Suez Crisis, 1956

The Malayan Emergency, 1948–1960

The Aden Emergency, 1963–1967

The Troubles, 19681998

The Falklands War, 1982

The Gulf War, 1990–1991

The Bosnian War, 1992–1995

The Kosovo War, 1998–1999

The Global War on Terrorism, 20012013

The War in Afghanistan, 2001–2014

The Iraq War and Insurgency, 20032011

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