World War II (1939–1945) was the largest and deadliest conflict in human history. It involved major nations across Europe, Asia, Africa, and the Pacific, and it reshaped global power for generations.

The war began in 1939 after Nazi Germany invaded Poland, which pushed Britain and France to declare war. Germany, Italy, and Japan formed the core Axis powers. The Allies included the United States, the Soviet Union, the United Kingdom, and many others.

The United States entered the war after Japan attacked Pearl Harbor on December 7, 1941. The conflict ended in 1945 with Germany’s surrender in May and Japan’s surrender in September. World War II led to the creation of the United Nations and started the Cold War era.