World War II
World War II (1939-1945) was the deadliest conflict in human history, fought between the Allied Powers and the Axis Powers across Europe, Asia, Africa, and the Pacific.
The war began in Europe on September 1, 1939, when Nazi Germany invaded Poland, prompting Britain and France to declare war. It expanded globally after Japan's attack on Pearl Harbor in December 1941 brought the United States into the conflict.
The war saw unprecedented devastation, including the Holocaust, in which Nazi Germany systematically murdered six million Jews and millions of others, and the only wartime use of nuclear weapons, when the United States dropped atomic bombs on Hiroshima and Nagasaki in August 1945.
The war ended with the surrender of Germany in May 1945 and Japan in September 1945, reshaping the global political order and leading to the creation of the United Nations to help prevent future conflicts.