A string of German attacks on merchant ships-culminating in the sinking of the British passenger ship Lusitania on May 7, 1915-led President Wilson to put pressure on the Germans to curb their navy. Unrestricted submarine warfare was first introduced in World War I in early 1915, when Germany declared the area around the British Isles a war zone, in which all merchant ships, including those from neutral countries, would be attacked by the German navy.
President Woodrow Wilson by agreeing to limit its submarine warfare in order to avert a diplomatic break with the United States.
On May 4, 1916, Germany responds to a demand by U.S.
