On February 1, 1917 Germany went back on its promises of the Sussex Pledge and resumed unrestricted submarine warfare and German U-Boats began to attack American ships in the North Atlantic.

What did the Sussex Pledge state?
The Sussex Pledge promised a change in Germany’s naval warfare policy. Sussex Pledge promised that:

• Passenger ships would not be targeted

• Merchant ships would not be sunk until the presence of weapons had been established, nor without provision for the safety of passengers and crew. 

Why did Germany abandon the Sussex Pledge?
Germany abandoned the Sussex Pledge because the German command believed that US resources and military operations were tied up with the 1910 Mexico revolution and the cross-border raids into New Mexico led by Pancho Villa and were convinced they could defeat the Allies by instituting unrestricted submarine warfare before the United States could enter the war.

What did the Sussex Pledge state?
The German Government notified the US Government of the that German naval forces had received the following order:

"In accordance with the general principles of visit and search and the destruction of merchant vessels, recognized by international law, such vessels, both within and without the area declared a naval war zone, shall not be sunk without warning and without saving human lives unless the ship attempts to escape or offer resistance".

Facts about Sussex Pledge
The following fact sheet contains interesting facts and information on Sussex Pledge.

WW1 began in Europe on July 28, 1914 but the United States remained neutral for over two years and entered WW1 on April 6, 1917.

On 4 February, 1915 Germany declared the seas around Britain a war zone that would be subjected to submarine warfare and that from 18 February, 1915 allied ships in the area would be sunk without warning.

The German announcement resulted in an angry and indignant reaction from the United States. Attacking civilian vessels without warning violated an international treaty that stipulated that military vessels had to reveal their intentions to merchant ships, and make provisions for the safety of the targeted ship’s crew and passengers, before sinking it.

Germany justified their policy of of unrestricted submarine warfare by claiming that many British merchant ships were actually warships in disguise and that their U-boats would be placed at great risk if they revealed themselves before firing.

On May 7, 1915 the British passenger ocean liner the Lusitania was sunk by a German U-Boat. A total of 1158 people were killed, including 148 Americans.

The sinking of the Lusitania  caused outrage in America and public opinion turned against Germany. President Wilson issued three diplomatic notes in May, June, and July 1915 affirming the rights of US citizens to travel safely at sea and warned that future sinkings would be viewed as "deliberately unfriendly."

On March 24, 1916 a German U-Boat (submarine) in the English Channel attacked what it thought was military ship that was on a mine-laying mission.

The ship was actually an English Channel passenger ferry called 'The Sussex' and was on the short voyage from Folkestone to Dieppe carrying 325 passengers with 53 crew members.

The Sussex ship was severely damaged by the U-Boat attack. Lifeboats were launched, but two of them capsized and many passengers were drowned. At least fifty people died and several Americans traveling on the Sussex were injured.

Although no US citizens were killed in the U-Boat attack, the incident enraged the American public causing a heated diplomatic exchange between the US and German governments which resulted in the "Sussex Pledge"

The "Sussex Pledge" was made by Germany on May 4th 1916 to the United States giving assurances that passenger ships would not be targeted and that Merchant ships would not be sunk until the presence of weapons had been established and provisions made for the safety of passengers and crew. 

Less than a year later, on February 1, 1917 Germany went back on its promises in the Sussex Pledge and resumed unrestricted submarine warfare. German U-Boats began to attack American ships in the North Atlantic.

Two days later, on February 3, 1917 the cargo ship "The Housatonic" was the first American ship sunk by the Germans under their unrestricted submarine warfare

On February 3, 1917 President Wilson announced a break in diplomatic relations with the German government (considered a prelude to a declaration of war).

Breaking the Sussex Pledge led to the sinking of five more American merchant ships by German U-boats.

The cause of the US entry into WW1 were the provocative acts surrounding the sinking of the Lusitania and the breaking the Sussex Pledge together with other events such as acts of sabotage in America including the Black Tom Explosion and the serious diplomatic incident  referred to as the Zimmermann Telegram

The United States declared war with Germany and entered into World War 1 on April 6, 1917.

During WW1, 126,000 Americans died and 234,000 Americans were wounded. World War 1 ended on 11 November 1918.