Mediterranean and Middle East. Nearly all of the world's countries participated, with many nations mobilising all resources in pursuit of total war. Tanks and aircraft played major roles , enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war.
World War II was the deadliest conflict in history, resulting in 70 to 85 million deaths , more than half of which were civilians. Millions died in genocides , including the Holocaust , and by massacres, starvation, and disease. After the Allied victory, Germany , Austria , Japan , and Korea were occupied, and German and Japanese leaders were tried for war crimes.
In , the Soviets annexed the Baltic states and parts of Finland and Romania. Through campaigns and treaties, Germany gained control of much of continental Europe and formed the Axis alliance with Italy , Japan , and other countries.
In June , Germany led an invasion of the Soviet Union , opening the Eastern Front and initially making large territorial gains. Japan conquered much of coastal China and Southeast Asia, but its advances in the Pacific were halted in June at the Battle of Midway. In late , Axis forces were defeated in North Africa and at Stalingrad in the Soviet Union, and in their continued defeats on the Eastern Front, an Allied invasion of Italy , and Allied offensives in the Pacific forced them into retreat on all fronts.
The war in Europe concluded with the liberation of all German-occupied territories ; a joint invasion of Germany by the Western Allies and the Soviet Union, which culminated in the fall of Berlin to Soviet troops; and Germany's unconditional surrender on 8 May The U. Japan announced its unconditional surrender on 15 August, and signed a surrender document on 2 September World War II changed the political alignment and social structure of the world, and it set the foundation of international relations for the rest of the 20th century and into the 21st century.
