Modern World History (1914-current)

World War II was a global conflict that stemmed from a European-centered conflict that began in Europe in 1939 and a Sino-Japanese conflict that began in eastern Asia in 1937. The ensuing warfare directly affected much of Europe, North Africa, eastern and Southeast Asia, and indirectly affected all other world regions.

World War II was the largest conflict in world history, given the amount of troops and war matériel and the vast scale of combat fronts in eastern Asia, the Pacific, Eurasia, and northern Africa. The eastern front, where 6 million Soviet troops confronted 4 million Axis troops over a span of thousands of miles from the Arctic to the Caucasus Mountains, stands as a stark example of the immense scale of the conflict. Moreover, the war led to millions of civilian deaths through the destruction of cities by strategic aerial bombardment (e.g., then rebombing of German and Japanese cities by Allied air forces, the dropping of the atomic bomb on Hiroshima and Nagasaki) and artillery attacks by invading armies (e.g., the German blitz on Polish cities, the Soviet siege of Berlin of 1945).

The development of technologies that offered new methods of killing (e.g., Zyklon-B poison gas, the atom bomb, and B-17 Boeing Flying Fortress bombers) also characterized the nature of this global conflict. Moreover, the deliberate systematic destruction of civilians by military authorities in tandem with civilian collaboration, most notably in the Holocaust, was an example of the vast scale of destruction of human life made possible in the context of total war. In contrast, those areas least affected by war, such as the Americas and sub-Saharan Africa, were still heavily involved, providing troops and/or material to the Allies.

From CREDO The Second World War in World History Encyclopedia
Landing on the Coast of France on D-Day