Why did the US become isolationist after World War 1?
The Great Depression and the memory of devastating losses in World War I contributed to moving American public opinion and policy toward isolationism. Isolationists advocated non-involvement and non-entanglement in international politics.
The US wanted to maintain a policy of isolationism after World War 1 and did not want to involve itself anymore in European affairs that would drag the US into international disputes that were not of their interest. They did not want American troops to be sent to Europe in order to settle European disputes.
Also, after World War 1, there was a growing concern that foreigners would take American jobs – because they were able to accept lower pay. As a result, the United States became economically (trade) and politically separated from the rest of the world (by staying out of the affairs of other countries). America decided they did not need the rest of the world.