The major global conflict that occurred between 1939 and 1945 was World War II. This devastating war involved most of the world's nations, including the great powers divided into the Allies and the Axis. It was marked by significant events, including the Holocaust, the use of atomic bombs on Hiroshima and Nagasaki, and critical battles such as Stalingrad and Normandy. World War II resulted in an estimated 70-85 million fatalities, making it one of the deadliest conflicts in human history. The war fundamentally reshaped international relations, leading to the establishment of the United Nations and the onset of the Cold War.