Why was Zimmermann telegram important in world war 1?

The Zimmerman Telegram was the catalyst that brought the United States into World War I. The Allied nations intercepted a German telegram to Mexico in which Germany promised to support Mexico in a bid to recapture territory it lost to the United States in the previous century (namely, California, Arizona and New Mexico) the Mexicans would go to war with the United States to distract it from joining the War in Europe. Whereas the German policy of unrestricted submarine warfare bothered President Woodrow Wilson more than any foolhardy proposition of Mexico, public fury against the Germans gave Wilson what he needed to finally join the side of the Allies and thus bring the United States into one of the most devastating wars in history.