Answer:
It was the tipping point that convinced the United States to join the war efforts.
Step-by-step explanation:
The Zimmerman Telegram was a telegram that promised that if the United States entered the war that Mexico would join Germany in their fight so that they could reclaim New Mexico, Arizona, and Texas back from the US. British code breakers intercepted the telegram and it never made its way to the intended person. However, once decoded, it was enought for America to put their foot into the war.