During the first two years of the war in Europe, President Wilson had carefully avoided making any commitments on behalf of the United States. He was careful, even, to avoid assessing blame, insisting that the war was a European matter that didn’t concern the United States, that our national security was not in danger. The U.S. had always been a great melting pot, and especially after the waves of migration from Europe at the turn of the century it was natural that immigrants would support their mother countries in the war. Rival opinions and conflicts would tend to arise, even during the newsreels shown in the movie theaters before the feature film. Wilson tried to minimize such tension, ordering a special notice to be shown before the newsreels: “It would be a patriotic act in the interest of the neutrality of the nation and the peace of mankind if the audience in this theatre would refrain during the showing of pictures connected with the present war from expressing either approval or disapproval.”

To the German Minister to Mexico
Berlin, January 19, 1917
…We propose an alliance on the following basis with Mexico: That we shall make war together and together make peace. We shall give general financial support, and it is understood that Mexico is to reconquer the lost territory in New Mexico, Texas, and Arizona….

During the presidential election of 1916, concerns with Mexico were the paramount military issue. As far as Europe was concerned, Wilson ran on a platform of continued neutrality, which generally reflected the popular sentiment. When the British ocean liner Lusitania was sunk by a German U-boat in May 1915, killing 1,200 people on board, including 128 Americans, Wilson had responded with calm, and managed to negotiate an understanding with Germany that neither ships of neutral countries, nor large passenger liners of any nationality, would be attacked.

After Wilson won reelection in 1916, however, two events occurred which changed public opinion and also changed Wilson’s attitude. The first was a declaration by Germany in January 1917 that it would no longer restrict submarine warfare, and would attack any target which it believed was in its interest to destroy. The second was the British interception of a coded telegram from Germany’s foreign minister, Arthur Zimmermann, to the German Ambassador to Mexico offering United States territory to Mexico in return for joining the German cause. The telegram had such an impact on American opinion that, according to David Kahn, author of The Codebreakers, “Never before or since has so much turned upon the solution of a secret message.” The telegram was sent at the end of January 1917, but in an effort to protect their intelligence from detection and to capitalize on growing anti-German sentiment in the United States, the British waited until late February to present the telegram to Wilson. The American press published news of the telegram on 1 March 1917. On 6 April 1917, the United States Congress formally declared war on Germany and its allies.