World War II, often abbreviated as WW2, was a global conflict that lasted from 1939 to 1945. It was the deadliest conflict in human history, involving the majority of the world's nations—including all of the great powers—organized into two opposing military alliances: the Allies and the Axis.
The war's roots are often traced to the aftermath of World War I and the harsh conditions imposed on Germany by the Treaty of Versailles. Economic depression, political instability, and the rise of nationalist movements in Europe set the stage for conflict. The Munich Agreement in 1938, where Britain and France appeased Adolf Hitler by allowing Germany to annex Sudetenland, did not prevent the war but rather delayed it.
The war in Europe concluded with the German surrender on May 7, 1945. In the Pacific, the war ended after the atomic bombings of Hiroshima and Nagasaki by the United States, leading to Japan's surrender on September 2, 1945.
The war resulted in an estimated 50 to over 85 million fatalities, both military and civilian. It led to significant changes in the political landscape, including the emergence of the United Nations, the division of Germany, the start of the Cold War, and the decolonization movement in Africa and Asia.