Two significant events that shifted America's neutral stance and led to its involvement in World War One were the sinking of the Lusitania and the interception of the Zimmermann Telegram. The Lusitania was a British passenger liner that was torpedoed by a German U-boat in May 1915, resulting in the deaths of 128 Americans among the 1,198 passengers. This incident fueled anti-German sentiment in the United States and highlighted the dangers of unrestricted submarine warfare, prompting calls for a more active response from the U.S. government.
The second pivotal event was the Zimmermann Telegram, sent in January 1917 by German Foreign Minister Arthur Zimmermann to Mexico, proposing a military alliance in the event that the U.S. entered the war against Germany. The British intercepted and decrypted the message, then shared it with the U.S. government, which caused outrage among the American public and increased support for entering the war. Together, these incidents dramatically shifted public opinion and pushed the U.S. government towards declaring war on Germany in April 1917.