Why is the Zimmerman telegram considered a major cause of the US entering World War 1?

The Zimmermann Telegram is considered a major cause of the U.S. entering World War I because it revealed Germany's attempt to incite Mexico to join the war against the United States. Sent in January 1917, the telegram proposed a military alliance between Germany and Mexico, promising to support Mexico in reclaiming territories lost to the U.S. This aggressive maneuver stirred public outrage and shifted American sentiment towards intervention, ultimately contributing to the U.S. decision to join the Allies in April 1917.