The significant global event that took place from 1939 to 1945 involving multiple nations was World War II. This conflict, marked by the struggle between the Axis Powers, including Germany, Italy, and Japan, and the Allied Powers, led to historic battles and widespread atrocities, including the Holocaust. World War II drastically altered the global political landscape, ending with the establishment of the United Nations and setting the stage for the Cold War. The war had profound effects on international relations, national boundaries, and played a significant role in decolonization movements worldwide.