World War II began in 1939 and ended in 1945. The war began in Europe on Sept. 1, 1939, when Germany invaded Poland. The war in the Pacific began when the Japanese navy attacked Pearl Harbor on Dec. 7, 1941.
In Europe, the war ended when German forces unconditionally surrendered on May 7, 1945. The Pacific war continued for several more months, due to the Japanese refusal to surrender. In August 1945, the United States dropped atomic bombs on the cities of Hiroshima and Nagasaki. The war officially ended with the signing of the surrender documents on Sept. 2, 1945.