What event marked the U.S. entrance into World War I?

The United States entered World War I primarily due to the discovery of the Zimmerman Telegram, which played a pivotal role in shifting public opinion and government policy toward war. This telegram, sent by German Foreign Minister Arthur Zimmerman to Mexico, proposed a military alliance between Germany and Mexico in the event that the U.S. entered the war against Germany. It promised Mexico the territories of Texas, New Mexico, and Arizona upon victory.

The interception and publication of this telegram outraged the American public and increased anti-German sentiment, making it difficult for the U.S. government to maintain its neutral stance. As a result, President Woodrow Wilson was compelled to ask Congress for a declaration of war against Germany, which was granted on April 6, 1917.

In contrast, the sinking of the Lusitania, while significant because it resulted in the loss of American lives and contributed to the anti-German sentiment, occurred earlier in 1915 and was not the direct catalyst for America's entry into the war. The Treaty of Versailles was established at the end of the war and thus could not have been a factor in the U.S. entering the conflict. The Russian Revolution, although it impacted the dynamics of the war and the subsequent peace negotiations, did not serve