World War II, like its predecessor WWI, was a total war. Nations fighting in the war used all available power and resources to mobilize their societies for war. 

The regions that were occupied by Nazi Germany were ruthlessly exploited for the German war effort: foodstuffs, raw materials, and war stocks were stolen. Members of the native population were drafted for forced labor in war industries or military construction projects. Millions more were deported to Germany to be used as forced laborers in German war industries or agriculture. German rule in Poland was extremely harsh. German authorities regarded the Polish population as a supply of forced laborers. The Germans destroyed Polish cultural and scientific institutions and plundered national treasures. In occupied western Europe, far milder policies were followed. "Germanic" countries like the Netherlands were ultimately slated to become part of Germany. Other countries, especially France, were to be kept dependent on Germany.

On December 7th, 1941, Japan attacked Pearl Harbor in Hawaii. President Franklin Roosevelt called it 'a day that will live in infamy' and brought the United States into World War II. While the United States had allies like Great Britain and the Soviet Union on their side, these countries were too busy fighting Nazi Germany to assist with Japan. So the U.S., nearly by itself, took island after island from the Japanese taking terrible losses; however, the Japanese would lose more. Finally, the U.S. made its way to Japan itself.