Answer: Germany's policy of unrestricted submarine warfare can take more credit for that. But the telegram was useful for convincing the American public that it should be sending its men over to Europe to fight. The telegram had proved the perfect justification for a change of policy and to convince some of the skeptics. Also, on February 1917 the telegram sent by the German foreign secretary, Arthur Zimmermann, to the German minister in Mexico. The telegram suggested that in the event that Germany and the US went to war, Mexico would regain "lost territories" in the southwest if it declared war on the US.
