Why was America unwilling to enter the Second World War? What led to its entry? Explain.

USA was unwilling to face all the economical problens the the first world war has caused once again. But it colud not stay out of the war for long. Japan was expanding it's power in the east. It had occupied Indo-China and wa planning to attack on USnaval bases in the Pacafic. When Japan expanded its its support to Hittler and boombed the US base at Pearl Harbour, the US entered the second World War.