World War II (1939-1945)

World War II remains the deadliest conflict in history, causing 70 to 85 million deaths—3% of the world's 1940 population. This catastrophic toll surpasses #2 by over threefold. Its profound consequences, including the Holocaust, the United Nations, the state of Israel, the Cold War, the dawn of nuclear weapons, decolonization across Asia and Africa, the Marshall Plan, and the European Union, reshaped the global order. The American-led international system governing affairs since 1945 is a direct legacy, making its impact more enduring than any conflict before or since.