Why did the U.S. not join the League of Nations?

The choice highlighting isolationism and partisan politics provides important insight into the reasons for the U.S. decision not to join the League of Nations. After World War I, the United States was experiencing a strong sentiment of isolationism, where many Americans believed that the country should avoid entangling alliances and focus instead on domestic issues. This perspective was closely linked to a widespread desire to disengage from European conflicts that had previously led to extensive American involvement in warfare.

Partisan politics also played a critical role. The proposal for the U.S. to join the League was championed by President Woodrow Wilson, who was a Democrat. However, opposition to him came primarily from the Republican Party, particularly from influential figures like Senator Henry Cabot Lodge. This partisan divide meant that even if there were some support for the League, the political landscape became polarized, making it difficult to achieve the necessary unanimous consent for U.S. participation.

In summary, the confluence of isolationist sentiment and the contentious political climate ultimately led to the U.S.'s decision to remain outside the League of Nations, reflecting a broader reluctance to engage in international organizations during that period.