The sinking of the RMS Lusitania by a German submarine in May 1915.
The event that finally convinced the United States to join World War I was the sinking of the British passenger ship RMS Lusitania by a German submarine on May 7, 1915. The attack resulted in the death of 128 Americans on board, which sparked public outrage and led to increased pressure on the U.S. government to enter the war. However, the United States did not officially join the war until April 6, 1917, after several other factors such as the resumption of unrestricted submarine warfare by Germany and the interception of the Zimmerman Telegram, which revealed a German plot to involve Mexico in a war against the United States, further exacerbated tensions between the two countries.
