Final answer:
The U.S. did not join the League of Nations due to the Senate's concerns over being drawn into foreign wars and losing the power to declare war, as well as skepticism regarding European control over the organization.
Step-by-step explanation:
The United States failed to join the League of Nations primarily because of concerns within the U.S. Senate about being drawn into foreign conflicts and losing constitutional control over war declarations. Senators, particularly from the Republican Party, were worried about the obligations that came with the membership, which would potentially compromise the nation's autonomy in deciding when to engage militarily. This hesitation was punctuated by a desire to avoid the horrors of another large-scale war and by skepticism over the motives and dominance of European powers within the League.
The Senate's opposition to the Treaty of Versailles, which included joining the League of Nations, was rooted in these fears, along with the belief that the League could embroil the U.S. in international disputes. Thus, despite President Woodrow Wilson's efforts and vision for the League as a means of promoting global security and preventing wars through collective action and diplomacy, the treaty was never ratified by the Senate. Consequently, the lack of U.S. participation undermined the effectiveness of the League, which struggled to mediate conflicts and was largely ineffective in preventing the outbreak of the Second World War.