Why the US Congress refuse to approve the treaty of Versailles or join league nations?

The U.S. Congress refused to approve the Treaty of Versailles primarily due to concerns over the League of Nations, which many senators believed could entangle the U.S. in international conflicts without Congressional approval. There was significant opposition led by Senator Henry Cabot Lodge, who argued that the League threatened American sovereignty. Additionally, there was a prevailing isolationist sentiment in the country after World War I, with many Americans preferring to avoid foreign entanglements. Ultimately, the treaty was rejected, and the U.S. did not join the League of Nations.