What was one of the main reasons for the U.S. entering World War I?

One of the primary reasons for the United States' entry into World War I was the interception of the Zimmermann Telegram. This telegram, sent by German Foreign Minister Arthur Zimmermann to the German ambassador in Mexico, proposed a military alliance between Germany and Mexico in the event that the United States entered the war against Germany. In exchange, Germany promised to support Mexico in recovering its lost territories of Texas, New Mexico, and Arizona.

When British intelligence intercepted and decrypted this communication in early 1917, they shared it with the United States, which caused public outrage and fueled anti-German sentiment. The revelation that Germany was attempting to incite conflict with the U.S. by encouraging Mexico to join the war against it had a significant impact on American public opinion and played a crucial role in swaying the U.S. government toward declaring war on Germany in April 1917. This incident highlighted Germany's aggressive strategies and contributed to the growing belief that the U.S. had a moral obligation to aid the Allies and uphold international stability.