Final answer:
The Spanish-American War's success bolstered President McKinley's popularity, highlighting his leadership and contributing to his re-election in 1900 by emphasizing patriotism and American expansionism.
Step-by-step explanation:
The role of the Spanish-American War in the 1900 U.S. presidential election was significant as it helped solidify the United State's status as a global military power and shaped public and political sentiment, affecting the election's outcome. The war increased the public's perception of the incumbent, President William McKinley, as a strong leader capable of expanding America's influence overseas. In addition to helping liberate Cuba from Spanish rule, the war's outcome included the annexation of Puerto Rico, Guam, and the Philippines, signaling the beginning of an American empire. The U.S. military's success during the war, despite its unpreparedness, and McKinley's management of the conflict bolstered his popularity. As a result, the war provided a platform for McKinley's re-election campaign that emphasized patriotism, strength, and American expansionism.