Short Answer 
Yellow journalism, characterized by sensationalism and exaggeration in reporting, became influential during the late 19th century, especially prior to the Spanish-American War. This reporting style shaped public opinion by dramatizing foreign conflicts, notably leading to the U.S. declaration of war against Spain after the sensationalized sinking of the Battleship Maine.
Step 1: Understanding Yellow Journalism
Yellow Journalism is a style of news reporting that emphasizes sensationalism and exaggeration to engage readers. This approach became prominent during the late 19th century, particularly leading up to the Spanish-American War. It often included fabricated stories or exaggerated facts to evoke emotional reactions and boost newspaper sales.
Step 2: The Influence on Public Opinion
The reporting style of yellow journalism significantly swayed American public opinion regarding foreign conflicts. As tensions rose with Spain over Cuba, newspapers churned out eye-catching headlines that emphasized American fears. This created a profound sentiment among the populace that intervention was necessary to prevent Spain from becoming too powerful, portraying the conflict as a moral imperative.
Step 3: The Catalyst for War
A critical event in this context was the sinking of the Battleship Maine in Havana Harbor on February 15, 1898. Yellow journalists sensationalized this incident, implying direct Spanish culpability, which escalated tensions. As public outcry grew due to these exaggerated reports, the United States ultimately declared war on Spain, marking a pivotal moment in American history.