Why wasnt the US part of the League of Nations when it first started?

The United States was not part of the League of Nations when it was established in 1920 primarily due to political opposition within the U.S. Senate. President Woodrow Wilson, a key proponent of the League, faced significant resistance from Republicans who were concerned about entangling alliances and the League's potential to compromise U.S. sovereignty. Despite Wilson's efforts to promote the League, the Senate ultimately rejected the Treaty of Versailles, which included the League's covenant, leading to America’s absence from the organization.