The US followed isolationism after WW1 because the public didn't want to be apart of another war which concerned Europe, and a war looked inevitable. Although the US hadn't suffered nearly as much as France or Britain as a result of WW1, the public felt that their troops shouldn't die because of a war in Europe. Because the US is a democracy, the government had to follow public opinion.
This is my understanding of it, hope it helped:)
While the US was isolated from world affairs, countries like Japan, Italy and Germany aggressively invaded other countries and built up their militaries. With no country willing to stop them, World War II was bloodier and longer than it could have been if these countries had been stopped earlier.
World War II
Neutrality and Isolationism were the American policies when World War I began. They kept the country out of the fighting, but it did not impede the sale of US goods to nations involved in the war.
Isolationism
Isolationism
The answer you seek is isolationism. This is the policy of not forming alliances.
World War 2.
Isolationism.
Isolationism.
World War I
World War I
World War I
Declared war on Japan after Pearl Harbor invasion.
'Isolationism'
World War II
Neutrality and Isolationism were the American policies when World War I began. They kept the country out of the fighting, but it did not impede the sale of US goods to nations involved in the war.
Isolationism .
Fear of communism