The United States abandoned its policy of neutrality and entered World War I for various reasons. The first reason was Germany's unrestricted submarine warfare against American ships, which resulted in the sinking of the Lusitania and other U.S. vessels, causing the death of many American citizens. This act violated U.S. neutrality and prompted the American government to declare war on Germany.
The second reason was the Zimmerman Telegram, which was intercepted by British intelligence and revealed Germany's plan to persuade Mexico to declare war against the United States. Germany promised to support Mexico in recovering its lost territories, including Texas, New Mexico, and Arizona. This revelation angered the American public and government, leading to a declaration of war against Germany on April 6, 1917.
Overall, the combination of unrestricted submarine warfare and the Zimmerman Telegram made it impossible for the United States to maintain its neutrality and compelled it to enter World War I.