When World War I broke out, the United States stood on the side and decided it was a war not for it to wage. For two and a half years, the US remained a neutral country until, in 1917, things began to shift, and the country was being drawn into the conflict, especially when Germany declared its unrestricted submarine warfare that permitted the attacks of their U-boats to torpedo ships regardless of their military status and country of origin. The last straw was said to be a telegram sent by Germany to Mexico.

Germany’s Underground Works

Perhaps for the Germans, the best place to hide was right under their (future) enemy’s nose, so even before they declared unrestricted submarine warfare, they started their diplomatic scheme in motion through a secret letter sent by the German foreign secretary Arthur Zimmermann in 1917. The letter was intended for Heinrich von Eckardt, the German minister in Mexico. The note’s scandalous content stated his plan of negotiating a military partnership with Mexico if the United States entered the war on the side of the Allied forces. They would propose that Mexico would be free to annex a portion of the American Southwest territory in exchange for launching an attack on the US. Part of the letter said,

We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor despite this to keep the United States of America neutral. In the event of this not succeeding, we make Mexico a proposal of alliance on the following basis: make war together, make peace together, generous financial support, and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona.

Zimmermann Telegram as Received by the German Ambassador to Mexico. [Source: docsteach.org]
Germany had lost its transatlantic telegraph cables earlier in the war when the British Royal Navy cut through them, leaving the Germans with no way of communicating privately between Berlin and North America. Still, the neutral United States agreed to send the letter on the condition that the contents were only diplomatic instructions and nothing more, unaware that its content was a threat to its security. On January 16, 1917, the telegram was handed to the US ambassador to Germany, James Gerard. He dutifully wired the letter to Copenhagen, where it was again transmitted to London and then to the German embassy in Washington. The letter reached Eckardt’s hands by January 19.