Final answer:
American Imperialism clashed with the fundamental U.S. belief in democracy and freedom and prompted the opposition of the Anti-Imperialist League, which saw empire-building as antithetical to American democratic principles.
Step-by-step explanation:
American Imperialism efforts, which aimed to extend the country's influence and control over other territories, often clashed with a central belief of the United States: the importance of democracy and freedom. The notion of empire-building challenged the country's founding principles which were centered on liberty and democratic ideals. Throughout history, figures like Thomas Jefferson promulgated the concept of an "empire of liberty", which aimed to spread democratic principles rather than to conquer and rule. Yet, the actions during the era of American Imperialism, such as the Philippine Insurrection and involvement in the Caribbean and Pacific, seemed to contradict these ideals, as they more closely resembled the oppressive nature of old empires like the Roman Empire. This clash of principles ignited considerable opposition domestically from groups like the Anti-Imperialist League, which included prominent figures who believed that the project of building an empire ran counter to the core democratic values of the United States.