Final answer:
The United States entered World War I after Germany sank U.S. merchant ships.
Step-by-step explanation:
The United States was led into World War I after Germany sank U.S. merchant ships. This event, known as the sinking of the Lusitania, occurred in 1915 and was a major factor in the U.S. decision to enter the war. The sinking of other U.S. merchant ships by German submarines also contributed to the American declaration of war in 1917.
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