Final answer:
Yellow press sensationalism most influenced U.S. governmental actions during the Spanish-American War.
Step-by-step explanation:
The event in U.S. governmental actions most influenced by yellow press sensationalism was the Spanish-American War in 1898. Media magnates William Randolph Hearst and Joseph Pulitzer used yellow journalism to agitate for war, sensationalizing coverage of Spain's crimes in Cuba and the explosion of the American battleship Maine. The exaggerated and often inaccurate reporting stirred up public emotion and led to increased support for U.S. military intervention in the war.