Perhaps the view of the U.S. entering WWI turned into most promising after the ripple effect of events after the sinking of the Lusitania. Each event made the United States weaker for entering the war and lastly there was no proper way to stay neutral. The instant cause of America's entry into World War I in April 1917 was the German announcement of unrestricted submarine warfare, and the following sinking of ships with Americans on board the Lusitania. The effects of the war were widespread throughout the world and can be traced for generations after the war.
The unrestricted submarine warfare was a sort of naval warfare in which submarines submerged merchant ships without notice. Even though the submarine was provided with powerfully lethal danger and larger odds of survival against its enemies, it was also measured by many as an important obstacle of the rules of war, specifically when working against neutral country vessels in a combat zone.
On May 7, 1915, a British vessel, the Lusitania, is torpedoed without notice by a German submarine off the south coast of Ireland. Within 20 minutes, the ship sank into the Celtic Sea. Out of 1,959 passengers and crew, 1,198 people were drowned, including 128 Americans. The outbreak provoked considerable anger in the United States, but Germany secured the act by mentioning that they had given out several warnings of its aim to attack all vessels that arrived in war zone around Britain. Dreading the United States entry into World War I, Germany tried to calm the United States by issuing, the Sussex pledge, on May 4, 1916, which undertook a change in Germany's naval warfare policy. The main elements of this pledge were that passenger vessels would not be targeted, merchant ships would not be submerged until...