True. The sinking of the Lusitania was one of the causes for the US to join the war. The attack on the Lusitania, a British passenger liner, by a German submarine in 1915 was a key moment in the lead-up to US involvement in World War I. The sinking of the ship, which resulted in the deaths of 1,198 people, including 128 Americans, outraged public opinion in the US and helped to turn the tide of public opinion in favor of joining the war.