How many years did the US fight in World War 1?

Answer 1

The USA entered the war in April 1917, and had troops in France from October 1917 to November, 1919, a little over 2 years. The war had begun in July, 1914.

Germany had resumed its 'Unrestricted Submarine Warfare', where it basically sank any ship travelling to an allied country like France or Britain (this included passenger ships). Germany had thought the US would get involved because the Germans sank the British passenger ship the RMS Lusitania in 1915, which was carrying 128 American passengers.

Because Germany thought the USA would now get involved in the war, they secretly asked Mexico to join the war on the German side. In a message through their US consulate, they offered to give Mexico money and to help Mexico get back the states of Arizona, New Mexico and Arizona, which Mexico had lost to the US in 1848. The British intercepted a coded telegram (the Zimmerman Telegram, from the German foreign minister) as it travelled from Germany to Washington, and the US took its revelation as a direct threat to them. Because of this, President Woodrow Wilson appealed to Congress, which declared war on Germany on April 6, 1917. The first troops arrived in France in June, 1917.