Over the years it has been a debated issue on whether the United States could have entered the war sooner and thus have saved many lives. Just after war broke out in Europe, Franklin Roosevelt got his cabinet to agree that the US should stay neutral in these affairs. Even so, Franklin Roosevelt thought the war was inevitable. American citizens did not want another war. The US did not enter the war until they were truly directly affected by the war. .
The Allies dismissed the aggression of the Axis, which consequently led to more aggression because the Axis then believed they could do whatever they wanted and not get punished. The isolationist mood the US took in the 1930's actually encouraged the Axis. Like any war when you are not the aggressor, but the defender, to enter the war you have to be provoked. In this case, Italy, Germany and Japan provoked the United States. Those countries have so far provoked America directly, but mildly, and those countries also defied America's interests and attacked America's allies. The US was afraid that the situation with the Axis could escalate so far that the Axis could take over the world or a good portion of it. The Axis's overall plan now was to try to dominate the world. In 1936 the US learned of the Axis plans. The US of course wanted to solve this problem peacefully.
Before Pearl Harbor was attacked, America was very scared that Japan might attack the US because of all the neighboring islands in the Pacific that were attacked. The US was right; Japan planned to attack America. On November 1, 1941 the Japanese leaders met to plan an attack on the US. They planned the battle to be in early December at Pear Harbor, where the pacific fleet was. .
Because of the Japanese aggression towards China, the US sided with China. The Japanese were very cruel to the people in the places the Japanese attacked. The Japanese brutality really upset the American public.