Although far from being the most prolonged military conflict in world history, World War II was easily the largest-scale, most far-reaching, and most destructive conflict in history. It killed more than 50 million people—many by mass murder—and physically and psychologically wounded more than 100 million more. Vast regions of Europe and Asia were laid waste by ground, air, and naval actions. Far removed from the main combat arenas in Europe and the Far East, the United States and Canada suffered little direct damage from the war, but both nations were heavily involved in supplying combat forces, ships, planes, weapons, and other military material to the Allied effort. The war ended with the unconditional surrender of Germany and Japan and redefined the international balance of power.
QUESTION: What factors contributed to World War II and how did it develop?