Which factor most directly contributed to the anti-imperialist sentiments following the Spanish-American War?

The provisions of the peace treaty ending the Spanish-American War played a critical role in shaping anti-imperialist sentiments in the United States. This treaty, known as the Treaty of Paris (1898), resulted in the U.S. acquiring territories such as Puerto Rico, Guam, and the Philippines. The transfer of these territories raised significant ethical and political concerns about America's role in imperialism.

Many Americans, especially anti-imperialists, argued that annexing these territories violated the fundamental principles of democracy and self-determination. They believed that the United States should not impose its governance on other peoples who had not consented to it. This perspective led to a prominent anti-imperialist movement that included influential figures, such as Mark Twain and Andrew Carnegie, who spoke out against imperialism as contrary to American values.

While other factors like economic interests in new territories and military presence in places like the Philippines contributed to the complexities of the period, they did not directly evoke such widespread moral outrage. Similarly, while some religious organizations may have expressed concerns about imperialism, it was primarily the implications of the Treaty of Paris that incited a broader and deeper political discourse, mobilizing public sentiment against the idea of an American empire.