Why did America enter WWII?

There are actually 5 main reasons for the US getting involved in the 2nd World War:

1. Germans started sinking US merchant ships taking supplies to England.
2. Japan's unreasonable demands on the United States (re- instating oil sales and dropping support of the Philippines and China)
3. German submarines beginning to shoot at US war ships
4. England and France are typically our allies so we were going to enter the war eventually anyway
5. Japan's attack on Pearl Harbor was the real reason why we entered the War. However 3 days later Germany declared war on us, even though we were not looking for any reason to fight.

Source(s):

Several articles and class notes