At what point in history did America enter into internationalism and become a world power?

America began its transition into internationalism and emerged as a world power in the late 19th century, particularly following the Spanish-American War in 1898. This conflict marked a significant shift as the U.S. acquired territories like Puerto Rico, Guam, and the Philippines, signaling its expansion beyond continental borders. The subsequent involvement in World War I further solidified its role on the global stage, establishing the U.S. as a key player in international politics and diplomacy. By the end of World War II, America was firmly positioned as a leading global power, shaping the post-war world order.