The causes of World War II are complicated. The immediate causes of World War II are generally held to be the Japanese attacks on China, the United States, the British and Dutch colonies and the German invasion of Poland. World War II began after these acts of aggression were met with an official declaration of war, armed resistance or both. | The causes of World War II are complicated. The immediate causes of World War II are generally held to be the Japanese attacks on China, the United States, the British and Dutch colonies and the German invasion of Poland. World War II began after these acts of aggression were met with an official declaration of war, armed resistance or both. |