The sinking of the Lusitania by a German U-boat greatly affected the United States of America. The deaths of US citizens travelling on a civilian vessel turned opinion in the neutral country against Germany. President Wilson has already sent two notes of protest to Germany, the second so strongly worded that it forced the resignation of William Jennings Bryan, the fiercely anti-war Secretary of State. He is replaced by his deputy, Robert Lansing, who favours a stronger line with Germany.
Germany’s replies to Wilson’s notes have been unsatisfactory. Now Wilson sends a third note of protest. The wording now is uncompromising. Germany’s assertion of freedom to attack civilian vessels without warning is rejected. Instead Wilson demands that Germany respects the freedom of the seas. The note finishes by saying that the US government will treat continued German attacks on civilian vessels as “deliberately unfriendly”.
The note retains the polite language of diplomatic correspondence, but Wilson has moved beyond mere protest. The third note is effectively an ultimatum. If Germany persists in its campaign of unrestricted submarine warfare then it will find itself at war with the United States.