Opposition from the Senate: The Treaty of Versailles required ratification by the United States Senate, but it faced strong opposition from a group of senators known as the "Irreconcilables." These senators argued that the treaty was too harsh on Germany, that it would weaken Europe and lead to future wars, and that it violated American sovereignty.
President Wilson's Illness: President Woodrow Wilson, who had been a key figure in negotiating the Treaty of Versailles, suffered a stroke in October 1919 and was unable to effectively lead the campaign for ratification. Wilson's illness left a vacuum of leadership and made it more difficult to build support for the treaty.
Isolationist Sentiment: There was a strong isolationist sentiment in the United States after World War I. Many Americans were reluctant to become entangled in European affairs and did not see the value of joining the League of Nations, which was created as part of the treaty.
Public Opposition: The American public was divided on the issue of ratification. Some supported the treaty, but others were critical of its terms and feared that it would lead to the United States being drawn into future conflicts.
Republican Control of the Senate: In the 1918 midterm elections, the Republican Party gained control of the Senate. Many of the newly elected Republican senators were opposed to the Treaty of Versailles and were unlikely to vote for its ratification.
In the end, the Senate failed to ratify the Treaty of Versailles by the required two-thirds vote, and the United States did not become a member of the League of Nations. The rejection of the treaty had significant consequences for the postwar order, as it contributed to the rise of nationalism, militarism, and the eventual outbreak of World War II.