The war that marked a shift in U.S. foreign policy towards greater involvement in global conflicts is the Spanish-American War of 1898. This conflict resulted in the United States acquiring territories such as Puerto Rico, Guam, and the Philippines, leading to an imperialist approach to international relations. The war signaled a readiness by the U.S. to exert its influence beyond North America, transitioning from a predominantly isolationist stance to one characterized by military and political engagement on the world stage.