why did the united states enter world war 1? what role did the zimmermann telegram play in that decision?

In 1917, Germany, determined to win its war of attrition against the Allies, announced the resumption of unrestricted warfare in war-zone waters. Three days later, the United States broke diplomatic relations with Germany, and just hours after that the American liner Housatonic was sunk by a German U-boat. The United States entered the war because of the Germans' decision to resume the policy of unrestricted submarine warfare, and Zimmerman, intercepted by the British, in which Germany floated the idea of an alliance with Mexico.