World War II was a global conflict that lasted from 1939 to 1945, involving the majority of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis. It was the most widespread war in history, directly involving more than 100 million people from over 30 countries.
The origins of World War II can be traced back to the aftermath of World War I, where the Treaty of Versailles imposed harsh penalties on Germany, leading to economic and political instability. The global economic depression of the 1930s further exacerbated tensions, allowing the rise of fascist regimes in several countries:
The war officially started on September 1, 1939, when Germany invaded Poland, prompting the United Kingdom and France to declare war on Germany two days later. This event marked the beginning of the European theater of the war.
The war in Europe ended with the unconditional surrender of Germany on May 8, 1945, known as V-E Day. In the Pacific, the war continued until August 15, 1945, when Japan surrendered following the atomic bombings of Hiroshima and Nagasaki, and the Soviet invasion of Manchuria. The formal surrender was signed on September 2, 1945, aboard the USS Missouri in Tokyo Bay.