How did the sinking of a British ship by a German submarine help bring the U.S. into World War 1?

The sinking of the British ocean liner RMS Lusitania by a German U-boat in May 1915 resulted in the deaths of 1,198 passengers, including 128 Americans. This act of unrestricted submarine warfare by Germany angered the American public and government, intensifying anti-German sentiment. Although the U.S. did not enter the war immediately, the Lusitania incident contributed to a growing desire to join the Allies against Germany, ultimately leading to U.S. involvement in 1917.