World War II (1939-1945) was a global conflict involving major world powers. It began when **Nazi Germany**, led by **Adolf Hitler**, invaded Poland, prompting Britain and France to declare war. The Axis Powers, including Germany, Italy, and Japan, fought against the Allied Powers, led by Britain, the Soviet Union, and the United States. Key events include Germany’s invasion of the Soviet Union, Japan’s attack on Pearl Harbor, and the D-Day landings in Normandy. The war ended with the defeat of the Axis Powers, after the atomic bombings of **Hiroshima** and **Nagasaki**, leading to immense global destruction and the establishment of the United Nations.