1. Sinking of the Lusitania:
In May 1915, a German U-boat sank the British passenger ship Lusitania, killing 1,198 people, including 128 Americans. This event provoked widespread outrage in the United States and increased public support for intervention.
2. Sussex Pledge:
Following the Lusitania incident, Germany pledged not to sink merchant ships without warning, provided that they did not carry armaments or resist. However, in March 1916, a German U-boat sank the French passenger ship Sussex, killing several Americans. This violation of the Sussex Pledge further eroded American neutrality.
3. Zimmermann Telegram:
In January 1917, the British intercepted and decoded a telegram from German Foreign Secretary Arthur Zimmermann to the German ambassador in Mexico. The telegram proposed an alliance between Germany and Mexico, with Germany offering to support Mexico in regaining its lost territories in the United States. This revelation angered many Americans and fueled support for declaring war on Germany.
4. Unrestricted Submarine Warfare:
In February 1917, Germany resumed unrestricted submarine warfare, sinking merchant ships without warning in an attempt to starve Britain into submission. This escalation of hostilities by Germany further strained relations with the United States and brought the country closer to entering the war.
5. Public Sentiment:
Public opinion in the United States had been shifting in favor of intervention for some time. Many Americans were appalled by the brutality of the war and felt a moral obligation to help the Allied Powers defeat Germany. The combination of the Lusitania sinking, the Sussex Pledge, the Zimmermann Telegram, and unrestricted submarine warfare galvanized public support for intervention and ultimately led to Wilson's decision to enter World War I in April 1917.