Loss of American Lives: German U-boats sank several merchant ships carrying American passengers and crew, resulting in the loss of innocent lives. The most notable incident was the sinking of the RMS Lusitania in 1915, which claimed the lives of over 100 Americans. These incidents generated widespread public outrage in the United States and increased pressure on the government to take action.
Violation of International Law: Germany's unrestricted submarine warfare violated international law, which prohibited the sinking of merchant vessels without warning and provision for the safety of passengers and crew. This disregard for international norms further angered the American public and raised concerns about the safety of American shipping.
Economic Impacts: The German U-boat campaign disrupted transatlantic trade and caused significant economic losses for American businesses. The sinking of merchant ships carrying vital supplies and goods led to shortages and price increases, affecting both the American economy and its allies.
Zimmermann Telegram: In early 1917, the British intercepted and decoded a telegram from German Foreign Secretary Arthur Zimmermann to the German ambassador in Mexico, proposing an alliance between Germany and Mexico against the United States. The telegram suggested that Mexico could regain territories lost to the United States in exchange for military support against the Americans. This revelation further inflamed American public opinion and fueled suspicions of German hostility towards the United States.
Public Sentiment and Propaganda: Pro-Allied propaganda efforts in the United States emphasized the atrocities committed by Germany, including unrestricted submarine warfare. This propaganda played a crucial role in shaping public perception and galvanizing support for intervention in the war.
The combination of these factors led to growing frustration and anger in the United States, eventually contributing to the decision to enter World War I on the side of the Allies in April 1917.