World War II began in 1939, marking a significant global conflict between the Axis powers—primarily Nazi Germany, Italy, and Japan—and the Allied powers, including the United States, the Soviet Union, and the United Kingdom. The war stemmed from unresolved issues from World War I, aggressive expansionism, and the failure of appeasement strategies. It led to vast military engagement across Europe, Asia, and Africa, fundamentally altering international relations and geopolitics. The conflict ended in 1945, resulting in the defeat of the Axis powers and significant social, economic, and political changes worldwide.