Which event marked the beginning of the U.S. as a global power?

The outcome of the Spanish-American War marked a significant turning point for the United States, establishing it as a global power. This conflict, fought in 1898, resulted in a decisive victory for the U.S. over Spain. The war demonstrated America's military capabilities and expanded its influence overseas. Following the war, the U.S. acquired territories such as Puerto Rico, Guam, and the Philippines, which not only marked a shift in American foreign policy but also signaled the country's entry into the ranks of imperial powers.

The annexation of Alaska, while important for resource acquisition and strategic positioning, did not immediately elevate the U.S. on the global stage in the same way. The signing of the Treaty of Paris in 1898 did conclude the war, but it was the war's outcome itself that showcased U.S. military strength and led to significant territorial gains. As for the declaration of war on Germany in 1917, this occurred later on and was part of the broader context of World War I, which bolstered U.S. power further but did not singularly initiate it. Thus, the conclusion of the Spanish-American War is accurately identified as the pivotal moment when the U.S. emerged as a recognized global power.