The Zimmerman Telegram was the telegram sent to the Mexican government on January 16, 1917 during the World War I (WWI) by Arthur Zimmermann, then Foreign Secretary of the German Empire. The telegram proposed that Mexican government should be an ally to the Germans forces if the United States joined the WWI. In addition, the telegram also suggested that if the Mexican government launched a pre-emptive strike against the United States, they would get the support of Germany. If they won the war, the Germans also promised Mexican government that they would get Arizona, New Mexico, and Texas.

Furthermore, the Zimmerman Telegram also urged that Mexican government should convince the Japanese forces to declare war against the Americans. The Telegram was sent during the Anti-German hype in the US, after the loss of 200 Americans lives from German submarine attacks ICO. The Telegram was intercepted by William Montgomery and Nigel de Grey who both worked at the British Naval Intelligence. The decryption of the Telegram was made possible by using a German diplomatic codebook that the British forces were able to acquire from the Germans.

However, the British government was in a dilemma – if they exposed the Zimmerman Telegram, the Germans would believed that their code was broken. The British were aware that there was an encrypted Mexican version of the telegram. They thought that if they could get hold of it, then they could make the Germans believe that the Zimmerman Telegram was acquired due to espionage activity happening in Mexico and not because of code breaking. The British government was able to get hold of the copy of the Mexican version of the Telegram and on February 23, it was delivered to Walter Page, then American ambassador to Britain who relayed it to then US President Woodrow Wilson.

On March 1 of the same year, copy of the Telegram was given to the US press. At first, the Americans did not believe the authenticity of the Telegram and took it as the US government’s way to convince the public that America should enter WWI. Furthermore, the German, Mexican, and Japanese diplomats denounced that such Telegram existed. However, after two days, the authenticity of the Telegram was confirmed to the American public and it became inevitable that the US joined the WWI. On April 6, 1917, the US Congress complied and brought the United States to join the WWI.