Republican Isolationists refused to ratify President Wilson's League of Nations after World War I because they feared it would draw the United States into future European conflicts. At the end of World War I, the US was only just begin to depart from its previous policy of foreign affairs, which was isolationism - staying out of other countries' affairs. The Isolationists feared that tethering the United States to the League of Nations would result in the US being required to come to the aid of an invaded European state at a later date.
The Republican Isolationists did not want any organization or mechanism that coud draw the U.S to a more integrated system in the world.
Explanation:
President Wilson's League of Nations was an international organization created by the Versailles Treaty on June, 28th, 1919. It established the bases for peace and the reorganization of international relations after World War I. In a way it was the first step towards the United Nations in the present.
