The U.S did not join the League of Nations following WWI. Even the the President of the United States at that time, Woodrow Wilson, was enthusiastic about the organization, they didn't officially join it. The reason why they didn't join it was because of isolationists in congress, in other words, people that didn't agree with what other people are interested in. Because of the war and all of the fatal deaths of Americans, people didn't want the U.S to be affiliated with Europe in any way.
