Unrestricted Submarine Warfare: Germany’s decision to resume unrestricted submarine warfare in the North Atlantic on 1 February 1917 was the final straw for the United States. The sinking of several US merchant ships, including the passenger liner Lusitania in 1915 and the Arabic, a British ocean liner carrying several Americans, in 1916, fueled public outrage and increased support for intervention in the war.
Zimmermann Telegram: In January 1917, the British intercepted and decoded a telegram sent by the German Foreign Secretary, Arthur Zimmermann, to the German ambassador in Mexico, Heinrich von Eckardt. The “Zimmermann Telegram” proposed an alliance between Mexico and Germany, promising to assist Mexico in regaining its lost territories in Texas, New Mexico, and Arizona. The exposure of this secret plot heightened American concerns about Germany’s aggressive intentions.
War Propaganda and Lusitania: The British engaged in extensive propaganda efforts in the United States to gain support for the war. They used emotional appeals, such as horrific accounts of German atrocities in Belgium and France, and portrayed the war as a fight for democracy against autocratic rule. The sinking of the Lusitania, in particular, was widely covered in the American media and galvanized public sentiment against Germany.
Economic Interest: The United States had significant economic ties with the Allies, particularly Great Britain and France, and their continued trade and financial support were vital to the American economy. The Allies owed large sums of money to American banks and the continuation of the war provided opportunities for American businesses to supply war materials.
Date of US Entry into World War 1:
The United States officially declared war on Germany on April 6, 1917. The declaration followed a series of diplomatic exchanges and escalating tensions between the two countries, including the Zimmermann Telegram and the continued sinking of American ships.