Why did the united states follow a policy of isolationism after world war 1

The people of the United States did not want to be involved in a war outside of their countries. Or foreign affairs as they called it.

This is because they did not need to join World War I but since Germany sunk the Lusitania, they wanted revenge against them. Thus they fought in a war they were not necessarily meant to (although in benefited their allies greatly.)

Hope this helps!