World War II was a global war that was under way by 1939, and ended in 1945. It involved a vast majority of the world's nations, including all of the great powers, eventually forming two opposing military alliances: the Allies and the Axis (轴心国). It was the most appalling and widespread war in human history, with innumerable people serving in military units. In a state of "total war", the major participants placed their entire economic, industrial, and scientific capabilities at the service of the war effort, erasing (消除) the distinction between civilian and military resources. Estimates for the total number of casualties of the war vary, because many deaths went unrecorded. Most suggest that some 60 million people died in the war. Many civilians died because of disease, starvation, and massacres.
The war ended with the total victory of the Allies over the Axis in 1945. World War II altered the political alignment (结盟) and social structure of the world. The United Nations was established to foster international cooperation and prevent future conflicts. The Soviet Union and the United States emerged as rival superpowers, setting the stage for the so-called Cold War, which lasted for the next 46 years. Meanwhile, the influence of the European great powers started to decline, while the decolonization (非殖民地化) of Asia and Africa began. Most countries whose industries had been damaged moved toward economic recovery. Political integration, especially in Europe, emerged as an effort to stabilize post-war relations.