World War II (1939 to 1945) was a global conflict that involved the majority of the world's nations, including the Allied Powers led by the United States, the United Kingdom, and the Soviet Union, and the Axis Powers led by Nazi Germany, Japan, and Italy. Triggered by the aggressive expansion of Adolf Hitler's Germany and by Japan's invasion of China, the war encompassed vast theatres of conflict, from Europe to Asia and the Pacific. World War II ultimately concluded with the unconditional surrender of the Axis Powers, reshaping the post-war world order.