In 1917, British Intelligence intercepted what became known as the Zimmermann Telegram. This was a communication from the German government to the Mexican government that attempted to convince Mexico to declare war on the U.S. to distract Americans from getting involved in World War I. Even though Mexican President Carranza ruled out any such action, the U.S. had evidence of a threat to its national security and declared war on Germany and its allies, but not on Mexico.