Why did they call the time between 1920-1941 the age of isolationism for the us ?

Ineed with this unit test 1. japan became a peaceful democratic nation relatively quickly after the end of world war 11 which step is not part of it post-war transformation -adopting a new constitution -disarming most of the military -giving women rights to vote -giving the emperor more political power 2. why did mao start the cultural revolution? -he thought government officials had promoted a very narrow view of communism -he wanted to speed up change and eliminate western, capitalist influence-he wanted to speed up the economy by promoting capitalism -he wanted to restore traditional chinese culture 3. what launched the korean war? -general macarthur led an invasion of north korea -north koreans, with stalin's approval, invaded south korea -south koreans tried to capture the government in p'yongyang-chairman mao urged the south koreans to invade north korea