World War I, 1914-18
When war began in Europe in 1914, Wilson immediately proclaimed the United States neutral. He urged the nation to be impartial "in thought as well as in action." However, Germany's use of submarines to attack ships the Germans thought to be carrying materials that would be helpful to the Allies created much hostility in the United States. Ill will increased after 114 United States citizens perished when the British liner Lusitania was sunk by a submarine in May, 1915. Wilson vigorously protested the sinking of such ships without provision for saving the lives of noncombatants. He resisted pressure to have the United States enter the war at that time, and obtained Germany's promise not to sink liners without providing protection for the passengers.
In the 1916 election, the Democrats used the slogan "He kept us out of war" to help win Wilson's reelection. However, Wilson had apparently already concluded that the United States would not be able to remain out of the war if it continued much longer. He thus sought to act as peacemaker, urging both sides to accept "peace without victory." His pleas were ignored.\
In January, 1917, Germany announced that unrestricted submarine warfare would be conducted against all ships destined for Allied ports. Several United States vessels were sunk. In March an attempt by German foreign minister Alfred Zimmermann to persuade Mexico to attack the United States, in the event that the United States should declare war on Germany, was revealed. The stage was thus set for Congress, at Wilson's request, to declare war on Germany on April 6, 1917.
United States manpower and material resources tipped the scales against Germany and the other Central Powers. The fighting ended on November 11, 1918, after Germany agreed to an armistice on Allied terms. The armistice was to remain in effect until peace treaties were signed.
The Treaty of Versailles was the most important of several treaties that resulted from the peace conference held in Paris in 1919. On the insistence of Wilson, who attended the conference, this treaty, in addition to ending the war with Germany, provided for creation of the League of Nations. The United States itself never became a member of the League, however, largely because of a growing sentiment for isolationism. The Senate, dominated by Republicans, did not ratify the Treaty of Versailles, because creation of the League was part of the treaty.