* The sinking of the Lusitania: The British passenger ship Lusitania was sunk by a German U-boat in May 1915, killing 1,198 people, including 128 Americans. This incident caused a great deal of outrage in the United States and helped to turn public opinion against Germany.
* The Zimmerman Telegram: In January 1917, the British intercepted and decoded a telegram from the German foreign secretary, Arthur Zimmermann, to the German ambassador in Mexico. The telegram proposed that Mexico and Germany should form an alliance against the United States. This revelation further angered Americans and made it seem as though Germany was planning to attack the United States.
* The unrestricted submarine warfare: In February 1917, Germany announced that it would resume unrestricted submarine warfare, meaning that it would attack any ship, including passenger ships, in the waters around Britain. This decision was a major turning point in the war and brought the United States into the conflict.
In addition to these specific incidents, there were also a number of other factors that contributed to the United States' decision to join World War I. These included:
* Economic ties to Britain and France: The United States had strong economic ties to Britain and France, and the war had disrupted these ties. This made it difficult for the United States to remain neutral.
* Idealism and the desire to make the world safe for democracy: Many Americans believed that the United States had a moral obligation to help the Allies defeat Germany and make the world safe for democracy.
* The fear of a German victory: Some Americans feared that a German victory would pose a threat to the United States. This fear was based on the belief that Germany was a militaristic power that would seek to dominate the world.
Ultimately, the United States' decision to join World War I was a complex one that was based on a number of factors. The sinking of the Lusitania, the Zimmerman Telegram, and the unrestricted submarine warfare were all important events that contributed to the decision, but they were also part of a larger context that included economic, political, and ideological considerations.