Final answer:
Opposition to President Woodrow Wilson and the Treaty of Versailles after World War I was rooted in concerns about the harsh treatment of Germany, support for imperialism, lack of self-determination for ethnic groups, and the potential loss of U.S. sovereignty.
Step-by-step explanation:
Herbert Hoover was a notable figure who criticized the economic ramifications of the treaty. Additionally, there was concern that the treaty supported imperialism rather than self-determination, as some national boundaries did not align with ethnic groups' aspirations. Ireland's independence was another contentious issue ignored in the treaty, causing dissatisfaction among many Americans.
Diverse political groups, including Republicans, conservative Democrats, and ethnic communities, voiced their opposition. Wilson's failure to consult U.S. senators in the peace process, severe reservations about the loss of sovereignty under the League of Nations, and the perception of Wilson acting unilaterally exacerbated the problem.
The disillusionment with the aftermath of the war, the shift towards isolationism, and the reluctance to entangle the U.S. in European politics and future conflicts also influenced public opinion and legislative decisions. Consequently, the United States never ratified the Treaty of Versailles nor joined the League of Nations, which weakened both the treaty's impact and the international influence of the League.