

The causes of World War II are debated, but contributing factors included the Second Italo-Ethiopian War, the Spanish Civil War, the Second Sino-Japanese War, the Soviet–Japanese border conflicts, the rise of fascism in Europe and rising European tensions since World War I. In the wake of the Axis defeat, Germany and Japan were occupied, and war crimes tribunals were conducted against German and Japanese leaders.

Tens of millions died due to genocides (including the Holocaust), starvation, massacres, and disease. World War II was by far the deadliest conflict in human history it resulted in 70 to 85 million fatalities, mostly among civilians. Aircraft played a major role in the conflict, enabling the strategic bombing of population centres and deploying the only two nuclear weapons ever used in war. The major participants in the war threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was a total war that directly involved more than 100 million personnel from more than 30 countries. It involved the vast majority of the world's countries-including all of the great powers-forming two opposing military alliances: the Allies and the Axis powers. World War II or the Second World War, often abbreviated as WWII or WW2, was a global war that lasted from 1939 to 1945.
