World War II

World War II was the largest armed conflict in human history, fought between the Allied powers — principally the United Kingdom, the Soviet Union, the United States, China, and France — and the Axis powers, led by Nazi Germany, Imperial Japan, and Fascist Italy. The war is conventionally dated from Germany's invasion of Poland on 1 September 1939 to Japan's formal surrender aboard the USS Missouri on 2 September 1945, though fighting in Asia began earlier with Japan's 1937 invasion of China, and some historians trace origins to Japan's 1931 occupation of Manchuria.

The conflict killed an estimated 70–85 million people, including civilians murdered in the Holocaust, in which Nazi Germany and its collaborators systematically killed roughly six million Jews alongside Roma, disabled people, Soviet POWs, and other targeted groups. Major turning points included the Battle of Britain (1940), the German invasion of the Soviet Union (Operation Barbarossa, 1941), the Japanese attack on Pearl Harbor (7 December 1941), the Battle of Stalingrad (1942–43), the D-Day landings in Normandy (6 June 1944), and the U.S. atomic bombings of Hiroshima and Nagasaki (6 and 9 August 1945).

The war's institutional legacy is central to modern international relations:

• The United Nations Charter was signed in San Francisco on 26 June 1945 and entered into force on 24 October 1945, with the five principal victors becoming permanent members of the Security Council.
• The Bretton Woods conference (1944) established the IMF and the institution that became the World Bank.
• The Nuremberg and Tokyo tribunals (1945–48) prosecuted war crimes, crimes against peace, and crimes against humanity, laying foundations for modern international criminal law.
• The 1948 Universal Declaration of Human Rights and the 1949 Geneva Conventions responded directly to wartime atrocities.

The war also precipitated decolonization, the division of Europe, and the onset of the Cold War.