When there were signs that an extra boost might be needed, it was decided to use the Zimmermann telegram. We intend to begin unrestricted submarine warfare on the first of February. Nevertheless, we will strive to maintain the neutrality of the United States of America. In case this does not succeed, we make a proposal for an alliance in Mexico on the basis of: make war together, make peace together, generous financial support and understanding on our part that Mexico will take back the lost territory in Texas, New Mexico and Arizona. Billing in detail is up to you. They will inform the president very secretly as soon as the outbreak of war with the United States of America is certain, adding the suggestion that he should invite Japan to join immediately on its own initiative, while serving as a mediator between Japan and us. Please draw the President`s attention to the fact that the reckless use of our submarines now offers the prospect of forcing Britain to peace in a few months. Signed, ZIMMERMANN On January 16, 1917, Zimmermann sent a secret message to the German minister in Mexico, Heinrich von Eckhardt. He asked Eckhardt to propose a German-Mexican alliance if the United States went to war The British Cryptography Office, known as „Room 40,“ decrypted the Zimmermann telegram and handed it over to the United States in late February 1917. On March 1, its scandalous content was injected into the front pages of the country`s newspapers. Diplomatic relations between Germany and the United States had already been severed in early February, when Germany resumed unrestricted submarine warfare and began hunting American ships in the Atlantic. While many Americans remained committed to isolationism — President Woodrow Wilson had just been re-elected with the slogan „He kept us out of the war“ — the Zimmerman figure now served as further evidence of German aggression. In connection with submarine attacks, he eventually turned the U.S.
government into favor of the fight. On April 2, 1917, President Wilson abandoned his policy of neutrality and asked Congress to declare war on Germany and the Central Powers. The United States would share its fate with the Allies four days later. What was left of skepticism was dispelled when Zimmermann himself took the strange step of confirming that he had sent it. A month later, America was at war. From there, it would finally be the 19th. Arrived at the German embassy in January to be decrypted, then transcoded and sent by a Western Union commercial telegraph office in Mexico, where she arrived the same day. This meant that, technically, all parties could claim that it had been decoded on U.S. territory. The Zimmermann Telegram was part of the Germans` efforts to transfer the transport of supplies and other war material from the United States to the Allied powers at war with Germany.  The main purpose of the telegram was to get the Mexican government to declare war on the United States in the hope of immobilizing U.S. forces and slowing down the export of U.S.
weapons.  The German high command believed it would be able to defeat the British and French on the Western Front and strangle Britain with unfettered submarine warfare before American forces could be trained and shipped to Europe in sufficient numbers to assist the Allied powers. The Germans were encouraged by their successes on the Eastern Front to believe that they would be able to divert large numbers of troops to the Western Front in support of their objectives. The Mexicans were willing to consider the alliance but rejected the deal after the Americans were informed of the telegram. But how could Britain use it – when would it show both that they broke German codes and that they received the message by spying on the very country it hoped to become its ally? Mexican President Venustiano Carranza has commissioned a military commission to assess Germany`s envisaged feasibility of a Mexican takeover of its former territories.  The generals concluded that it would be neither possible nor desirable to attempt such an undertaking for the following reasons: In this exercise of decoding a message, students decode a fictitious message with a simple substitute code. The telegram had proven to be the perfect justification for a change in policy and had convinced some of the skeptics. London bet that Germany`s use of unfettered submarine warfare – an attack on the merchant navy – would be enough to drag America into the war. The day before, German Foreign Minister Arthur Zimmermann had sent a message to the German ambassador in Washington. Tuesday marks the 100th anniversary of a remarkable success for British intelligence: but one that involved spying on the United States, and then a conspiracy with its senior officials to manipulate American public opinion. An encrypted message about the attack on the United States was actually relayed through U.S.
diplomatic channels. Public opinion in the United States was now wavering firmly in the direction of the United States` entry into World War I. On April 2, Wilson went to Congress to deliver a message of war. The United States officially entered the conflict four days later. Britain could then plausibly claim that it arrived at the embassy in this way, circumventing the problem of admitting that it was spying on its friends. The Zimmermann telegram as received by the German ambassador to Mexico The Zimmermann telegram had such an impact on American opinion that, according to David Kahn, author of The Codebreakers, „no other cryptanalysis has had such enormous consequences.“ He is of the opinion that „never before or since so much has been so focused on solving a secret message. Zimmermann`s office sent the telegram to the German embassy in the United States for further distribution in Eckardt, Mexico. It has traditionally been claimed that the telegram was sent via three channels: by radio and also via two transatlantic telegraph cables operated by neutral governments (the United States and Sweden) for the use of their diplomatic services, but it was found that two methods were used.
The Germans forwarded the message to the U.S. Embassy in Berlin, and it was then transmitted by diplomatic cable first to Copenhagen and then to London for transatlantic cable transmission to Washington.  Room 40 asked one of its contacts to obtain a copy of something sent from the United States to the German Embassy in Mexico. This provided another copy of the telegram. Most historians agree that American involvement in World War I was inevitable in early 1917, but the march to war was undoubtedly accelerated by an infamous letter from German Foreign Minister Arthur Zimmermann. On January 16, 1917, British codebreakers intercepted an encrypted message from Zimmermann to Heinrich von Eckardt, the German ambassador to Mexico. The letter gave the ambassador a now famous series of instructions: If the neutral United States went to war on the side of the Allies, Von Eckardt would have to turn to the Mexican president with the offer to forge a secret war alliance. The Germans would support a Mexican attack on the United States militarily and financially, and in return Mexico would be free to annex „the territory lost in Texas, New Mexico and Arizona.“ In addition, Von Eckardt was ordered to use the Mexicans as mediators to incite the Japanese Empire to join the German cause. .