Given that the japanese war against china began in 1937 and german aggression began in europe in 1936, why was it not until 1941 that the united states joined the war against the axis powers? was the decision to stay out of the war until 1941 a wise one on the part of the united states?

The United States was an isolationist country during these times. Most people alive still remember WW1 and do not want to have another overseas war. It was only when the Japanese sailed across the ocean to attack us did we get involved. It was a wise idea in the long run, giving the US time to slowly improve its tech and military somewhat while the european countries and china was being overrun. 

Divide each number then subtract