This was allegedly a communication sent by German chancellor Theobald von Bethmann-Hollweg to Mexican president Venustiano Carranza asking the latter to join the war on Germany's side.
Germany promised that after a British defeat Germany would join Mexico in a war against the US with the aim of recovering Texas and California, captured from Mexico in previous wars.
Both Mr Carranza and Mr Bethmann-Hollweg protested that the telegram was an obvious forgery, concocted either by WR Hearst, who had substantial investments in Britain which would become worthless in the event of a British defeat or, more probably, by the British secret service.
However, the US Congress preferred to believe Hearst's version of events, and promptly declared war on Germany - something that president Wilson had been reluctant to do.
Apart from his instinctive pacifism, he had secured his election victory by assuring German and Irish voters that he would not "pull England's chestnuts out of the fire."
Keith J Ackermann