What major global conflict was fought between 1939 and 1945?

The major global conflict fought between 1939 and 1945 is World War II. This war began with the invasion of Poland by Nazi Germany in September 1939 and involved most of the world's nations, including all of the great powers, which eventually formed two opposing military alliances: the Allies and the Axis. It was marked by significant events such as the Holocaust, the use of atomic bombs, and massive military engagements across Europe, Asia, and the Pacific.

The conflict ended in 1945 with the unconditional surrender of the Axis powers, which included Germany, Italy, and Japan. World War II had a profound impact on the course of history, reshaping political boundaries, economies, and international relations, and leading to the establishment of the United Nations in an effort to prevent future conflicts.

Other options refer to different conflicts: World War I occurred from 1914 to 1918, the Cold War was a prolonged period of geopolitical tension primarily between the United States and the Soviet Union after World War II, and the Korean War took place from 1950 to 1953.