Even though the united states refused to sign the versailles treaty, thereby isolating themselves diplomatically, they were still very much involved in the world how?

The United States played a big role in the world affairs even they didn't signed the Treaty of Versailles after world war 1 due to unequal and unjustifiable terms the Allied Powers wants to the Central Powers. They were involved in the creation of the League of Nations in which it is the predecessor of the United Nations and also in world economy and stock markets now rotate in the United States.