Which event marked a significant turning point in U.S. foreign policy in the early 20th century?

The Spanish-American War represented a significant turning point in U.S. foreign policy in the early 20th century because it marked the transition of the United States from a largely isolationist nation to one that was more involved in overseas imperialism and global affairs. The war, fought in 1898, primarily between the United States and Spain, resulted in the U.S. acquiring territories like Puerto Rico, Guam, and the Philippines. This expansion indicated a shift in the U.S. approach to international relations, moving towards becoming a colonial power and asserting influence in the Caribbean and the Pacific.

The outcome of the war catalyzed several subsequent developments in U.S. foreign policy, including the justification of interventionism in Latin America through the Roosevelt Corollary to the Monroe Doctrine and fostering relationships that would later influence U.S. actions during World War I and beyond. This new assertiveness laid the groundwork for the United States to take a more active role on the world stage, which represented a departure from earlier policies that emphasized non-involvement and territorial acquisition through continental expansion.