Some members of the US Senate voiced concerns about the potential erosion of American sovereignty. They argued that the League of Nations could infringe on the United States' ability to make independent foreign policy decisions. They worried that the League could entangle the United States in European conflicts and weaken its ability to act in its own interests.
Reservations About Article X:
Article X of the Covenant of the League of Nations called for its members to "respect and preserve as against external aggression the territorial integrity and existing political independence of all Members of the League." Critics of the treaty felt that this provision could obligate the United States to defend the territorial integrity of other nations, even if it did not have a vested interest in doing so. They argued that this could lead the United States into unwanted conflicts and could potentially put American soldiers in harm's way.
Opposition to Internationalism:
Some Senators were isolationists and were not in favour of the involvement of the United States in international organisations or entangling alliances. They argued that the United States should focus on its domestic affairs and not become embroiled in the complex political dynamics of Europe and the rest of the world.
Political considerations:
The Treaty of Versailles and the Covenant of the League of Nationwere closely associated with President Woodrow Wilson's administration, which was unpopular among many Republicans in the Senate. Some Senators opposed ratification as a way of undermining Wilson's legacy and limiting the power of the executive branch.
These concerns led a substantial number of Senators to oppose the ratification of the treaty and the covenant, ultimately resulting in the United States' rejection of the Treaty of Versailles and its decision not to join the League of Nations.