Unless the Imperial Government should now immediately declare and effect an abandonment of its present methods of submarine warfare against passenger and freight-carrying vessels, the Government of the United States can have no choice but to sever diplomatic relations with the German Empire altogether (1).
The Germans responded by temporally ceasing submarine warfare until 1917 when German Ambassador Berstorff announced the continuation of submarine warfare and ended diplomatic relations with the United States. However, military strategists predicted certain defeat for the Germans if America entered the war at this point. In an attempt to eliminate the threat of American involvement in Europe, Foreign Minister Alfred Zimmerman attempted to provoke Mexico and Japan into attacking the United States with the promise of German assistance after the European front was conquered. A message containing Zimmerman's intent was decoded by the British and sent to the US, further swaying Americans to action. Due primarily to submarine warfare and the Zimmerman note, President Wilson asked Congress for permission to go to war, and on April 6, 1917, congress officially declared it. President Wilson, along with many Americans, justified their involvement as "an act of high principle and idealism...[and]...as a crusade to make the world safe for democracy." (2)
While these are some of the main events, there are many other theories regarding why the US entered into World War I. Some propose that