How did submarine warfare impact the US Decision to enter the war?

Submarine warfare, particularly the unrestricted submarine warfare practiced by Germany, significantly influenced the U.S. decision to enter World War I. The sinking of civilian ships, including the Lusitania in 1915, resulted in American casualties and heightened public outrage. This aggressive tactic not only threatened American lives but also jeopardized U.S. economic interests and trade with Allied nations. Ultimately, the cumulative effect of these incidents swayed public opinion and government policy towards intervention in the war.