United States
The First World War started in Europe in 1914. The United States said it was neutral and did not join the war at first. Later, the Americans helped the British and French, even though many citizens, especially those from Ireland and Germany, were against it. In 1917, the United States joined the Allies. They helped defeat the Central Powers. At the end fo the war, many Americans did not want to stay involved in Europe.  The Senate did not approve the Treaty of Versailles (1919). The United States stayed out of the League of Nations. The country became more isolationist.