Between 1914 and the spring of 1917, the European nations engaged in a conflict that became known as World War I. While armies battled in Europe, the United States remained neutral. In 1916 Woodrow Wilson was elected President for a second term, largely because of the slogan "He kept us out of war." Events in early 1917 would change that hope.
In January of 1917, British cryptographers deciphered a telegram from German Foreign Minister Arthur Zimmermann to the German Minister to Mexico, von Eckhardt, offering United States territory to Mexico in return for joining the German cause. To protect their intelligence from detection and to capitalize on growing anti-German sentiment in the United States, the British waited to present the telegram to President Wilson. Meanwhile, frustration over the effective British naval blockade caused Germany to break its pledge to limit submarine warfare. In response, the United States severed diplomatic relations with Germany.