The epic global conflict known for impacting nations worldwide and lasting from 1939 to 1945 is World War II. This war involved most of the world's nations, divided into two opposing military alliances: the Allies and the Axis powers. It was marked by significant events, including the Holocaust, the use of nuclear weapons, and pivotal battles across Europe and the Pacific. The war reshaped international relations, leading to the establishment of the United Nations, the Cold War, and the reorganization of political boundaries. Its impact on society, economies, and cultures across continents remains profound and lasting.