Which direct communication contributed to U.S. involvement in World War I by proposing an alliance between Germany and Mexico?

The Zimmerman Note was a pivotal communication that directly influenced the United States' decision to enter World War I. In January 1917, British intelligence intercepted a secret telegram sent by German Foreign Minister Arthur Zimmermann to the German ambassador in Mexico. The message proposed a military alliance between Germany and Mexico in the event that the United States entered the war against Germany. In exchange for Mexico's support, Germany promised to help Mexico regain territories it had lost to the U.S. — specifically Texas, New Mexico, and Arizona.

The release of this telegram to the American public stirred significant outrage and fear, as it indicated a direct threat to U.S. sovereignty and security. The prospect of a German-Mexican alliance was alarming, and it played a crucial role in swaying public opinion in favor of entering the war. Thus, the Zimmerman Note is recognized as a key factor in pushing the United States to abandon its initial position of neutrality and engage in the conflict on the side of the Allies.