President Wilson demanded that the German government abandon its submarine warfare or the US would be forced to declare war. There were multiple instances in which U-boats destroyed passenger ships holding Americans, and this left many US citizens outraged. In May of 1915, a British passenger ship called Lusitania entered the war zone. A German submarine destroyed the ship with its missiles, killing about 1,200 people which included 128 Americans. Another instance was in March of 1916, when once again, German submarines fired upon a passenger ship. This time it was a French ship the Sussex, and several Americans were injured. Germans repeatedly attacked Americans and this cannot be left unanswered.