World War II

World War II (1939–1945) was the deadliest military conflict in human history and the defining catastrophe of the 20th century. An estimated 70 to 85 million people died — approximately 3% of the world's entire population at the time — making it the single largest loss of human life in any conflict before or since. Unlike World War I, where military casualties dominated, WWII killed more civilians than soldiers: bombing campaigns, deliberate genocide, famine, forced labor, and population displacement drove the civilian death toll above 50 million.

The war had two distinct but linked theaters. In Europe, Nazi Germany under Adolf Hitler systematically conquered most of the continent between 1939 and 1942. The invasion of Poland on September 1, 1939 triggered war with Britain and France. The fall of France in June 1940 left Britain isolated. Operation Barbarossa — Germany's invasion of the Soviet Union beginning June 22, 1941 — opened the war's most destructive front. The Eastern Front alone killed approximately 30 million people, combining military losses from both sides with the Nazi program of deliberate starvation, execution, and slave labor of Soviet civilians. Stalingrad, fought between August 1942 and February 1943, became the turning point: the Soviet victory broke the Wehrmacht's offensive capacity and began the long German retreat.

Parallel to the European theater, Japan pursued its own empire-building across East and Southeast Asia and the Pacific. Japan's invasion of China beginning in 1937 — technically before the world war's official start — killed an estimated 15 to 20 million Chinese civilians and combatants through combat, the systematic mass murder of the Nanjing Massacre, deliberate famine, and biological warfare experiments conducted by Unit 731. Japan's attack on Pearl Harbor on December 7, 1941 brought the United States into the war, transforming an already global conflict into a truly worldwide industrial war.

The Holocaust — Nazi Germany's systematic genocide of Jewish people and other minorities — stands as the most documented atrocity of the war and the clearest example of state-organized mass murder in human history. Between 1941 and 1945, approximately 6 million Jewish people (two-thirds of European Jewry) were murdered in gas chambers, mass shootings, and concentration camps. An additional 6 million Romani, disabled people, Soviet prisoners, and others were killed in the same apparatus. The Holocaust demanded and produced entirely new legal frameworks: international humanitarian law, the Genocide Convention, the Universal Declaration of Human Rights.

The war ended with the unconditional surrender of Germany on May 8, 1945 (V-E Day) and Japan on September 2, 1945 (V-J Day), following the atomic bombings of Hiroshima and Nagasaki — the first and only combat use of nuclear weapons. The postwar order produced the United Nations, the Nuremberg Trials (establishing individual criminal accountability for war crimes), the Marshall Plan's reconstruction of Europe, and the Cold War division of the world between American and Soviet spheres. No event in history has more completely reshaped global politics, international law, and the human conception of war's limits.