Woodrow Wilson
In 1917, Wilson entered the country in World War One. America was previously neutral, but German submarines kept sinking American ships sailing in British waters and even tried to encourage Mexico to invade the United States, which was the final straw for Wilson. World War One was a war between the Central Powers (Germany, Austria-Hungary, and the Ottoman Empire) and the Allied Powers (England, France, and Italy). America was on the Allies' side. The Allies won the war a year later.