The HMS Lusitania was a British ocean liner that was sunk by a German submarine during World War I. About 1200 people died- including over 120 Americans. The Germans claimed that the ship was secretly carrying ammunition and weapons, thereby making it a valid target for submarines, which the British denied. Decades later, the British government finally admitted that the Germans were correct, and the ship was in fact carrying ammunition.However, most Americans were not convinced by the German claim, and were understandably upset at the casualties. The US was not involved in World War I, but the sinking of the Lusitania was one of the major factors that caused the Americans to perceive Germany negatively, causing the US to start siding with the Allies. Some Americans (and a lot of British) even demanded that the US declare war on Germany, but President Wilson refused.As a result, Germany promised to end her policy of unrestricted submarine warfare. They would follow certain rules to only attack certain warships and ships that were definitely British and not cruise ships. Also, when attacking a non-warship, they would allow the crew to escape on life boats before sinking their ship.Because of Britain's devastating naval blockade, two years later Germany restarted unrestricted submarine warfare, which along with the Zimmermann Telegram, caused the US to finally declare war on Germany.