When President Woodrow Wilson implored congress for a “war to end all wars” that would “make the world safe for democracy,” he made reference to the incursion upon United States neutrality in the German Empire’s resumption of unrestricted submarine warfare. Such warfare had has its incitation’s of military intervention in Europe overruled by Anti-War lobbies before especially in cases like the May 1915 sinking of RMS Lusitania and the Thrasher Incident but these parties could not hold ground against mass public uproar. This uproar emanated from the notorious Zimmerman Telegram which ignited existing anti-German and anti-Mexican sentiment and led the President, who “Kept us out of the war” and was “Too proud to fight,” to declarewar upon the German Empire on the 6th of April 1917.
Arthur Zimmerman until the 6th of August 1917 was State Secretary for Foreign Affairs of the German Empire and a rather provocative fellow as his impressive resume toted involvement in plans to support rebellions in India and Ireland as well as the Bolshevik cause in Tsarist Russia. Making politico-military life difficult for the British Empire and her allies, does not lend surprise to why Zimmerman was requested to give Venustiano Carranza’s Mexican government a cause to extend Francisco “Pancho” Villa’s minor border conflict in New Mexico into more of a national hindrance. Zimmerman did this through his aptly name telegram as the abrogation of the Sussex Pledge of not attacking merchant ships without due warning was the only way German High Command saw of breaking the Royal Navy’s blockade stranglehold. This would’ve undoubtedly brought the US into the fray when their merchant vessels came under attack so in order to bypass American intervention, Zimmerman made his appeal to the Mexican government with the hope that US military resources would be tied up in a more domesticated altercation.
Unfortunately for the German Navy, Zimmerman’s compromises for an all-out war between the US and Mexico did not allow for the actual strategic implications such a conflict would incur. The content of the telegram describes how Germany would be prepared to enter into an alliance with Mexico while it would maintain a state of neutrality with the US. For further reassurance Zimmerman suggested that if this were to fail, Mexico should make common cause with Germany and persuade the imperial Japanese government to join the alliance against the US. While Japan was assisting the Entente powers in securing the West Pacific and Indian Ocean sea lanes against the Imperial German Navy, their relationship with the US was not so friendly when it came to their Chinese sphere of influence. As Mexico would have little to rely on, Zimmerman realised that he must give Mexico a reason to join the Axis cause and he found this in promising Mexico financial assistance plus the restoration of its former territories of Texas, New Mexico and Arizona which it had lost in the Mexican-American War of 1846-48. Now Zimmerman had set the trap, would Carranza take the bait?
Carranza, described as an intelligent and yet stubborn man who became the leader of northern forces opposed to the counter-revolutionary regime of Victoriano Huerta and led the constitutionalist faction to victory before his appointment as President in May 1917, did take the bait… almost. Carranza as a fierce nationalist did stand up to enormous economic and political pressures from the US so Zimmerman’s suggestion of reclaiming Mexico’s former territories did tempt him considerably. However, Carranza was the same man who disbanded the old Federal Army in 1914 after witnessing what it done to his predecessor Madero therefore showing his hand as a careful leader which he put into practice when setting up a military commission to assess Zimmerman’s suggestion. This is when the commission concluded with the aforementioned strategic implications which prevent them from even considering such an attack. The biggest concern held by the commission was that simply, the US was too much stronger militarily than Mexico was as we can tell from the best 1917 estimates we have that Carranza’s Constitutionalist army of 80,000 was largely outranked by the US standing army of 140,000. These estimates are very loose as Mexico was in the midst of its revolution at the time so we have to rely on American attempts to make sense of the vying factions and differing governmental reports. The commission goes on to report that even if there was some hope of a Mexican victory, reclaiming their lost territories would be difficult as they would need to accommodate a large well-armed English-speaking population.
It wasn’t just Domestic issues which plagued Zimmerman’s plan according to Carranza’s commission. Financial planning for a US invasion trickled dangerously into international waters as the commission realised that Zimmerman’s promise for financial support for the attack was unreliable and so would need sourcing from elsewhere. It was obvious that Germany at the time was in economic difficulty as British blockades meant it had to rapidly mobilize its civilian economy just for the war effort, let alone a state sponsored invasion of one the world’s largest military powers. It was made more obvious for Carranza as back in June 1916 the German government informed him that they were unable to provide the necessary gold needed to stock a completely independent Mexican National bank. The financial prospect was made no more promising for Mexico by the fact that the only other source of resources for a US invasion could come from the ABC coalition of Argentina, Brazil and Chile. Considering how the ABC coalition had come together in the 1914 Niagara Falls Peace Conference after the US occupation of Veracruz to prevent further American-Mexican conflict, Mexico receiving resources from the coalition and maintaining good relations would be impossible. It was for these domestic and international reasons why Carranza had to decline Zimmerman’s proposal in his January telegram on the 14th of April.
You are probably wondering how a secret communiqué like the Zimmerman telegram between Germany and Mexico managed to get into the hands of the US president and what did Britain have to do with it? Simply put, international diplomatic communication during the Great War was not clear-cut and the German Foreign Office had the misfortune of Zimmerman’s coded telegram passing through the most advanced cryptographic hub in the world. To understand fully how London got its hands on the message in the coded telegram, it is a good idea first to understand the telegram’s intended route. The telegram began its journey by being sent to the US embassy in Berlin before leaving for the US embassy in Copenhagen. After Copenhagen, the telegram was transmitted to the US embassy in London so the signal could be sent on to Porthcurno (Near Land’s End) for boosting across transatlantic lines. Once it had reached the German embassy in the US it was sent for re-transmission to the German ambassador to Mexico, Heinrich von Eckardt. Now its route may seem unnecessarily long but in light of Britain cutting Germany’s international cables at the outbreak of the war, using American diplomatic cables as sanctioned by President Wilson to encourage his peace-making mission was the only option available. It may also seem odd that a covert message concerning a potential attack on the United States would have its contents go unnoticed when it arrived in the States considering how a condition of using US diplomatic cables was to have all messages not in code. On the contrary, The US Ambassador to Germany, James W Gerard who had been asked to leave Germany the very same month as the telegram, was persuaded to accept the telegram in code before having it sent on to Mexico.
The question of how did London crack the telegram a day after Zimmerman had sent it all relies upon the Porthcurno relay. Any traffic which passed through that relay was copied to British intelligence and as it was coded, required the skills of the code breakers and analysts in Room 40 at the Admiralty. Cryptographers Nigel de Grey and William Montgomery of Room 40 using previous code captured in the Mesopotamian campaign and retrieved from the wrecked cruiser SMS Magdeburg to crack the code by the 12th of January. However, Room 40 chief William Reginald Hall refused to disclose it to the Foreign Office until 3 weeks later and even than he advised the Foreign Office not to send it to the US immediately. His reasoning for this was that it not only allowed his cryptographers time to decipher the entire message but he saw it as necessary because he needed to think of a way to not raise suspicion of eavesdropping on American diplomatic lines and he couldn’t let the Germans suspect that the British had broken their latest code. The story Hall successfully used was that the British obtained the ciphertext of the telegram from the Mexican commercial telegraph Office. In pairing this with re-encrypting the telegram in an older German code before sending it off, the US remained oblivious and the Germans at best only knew one of their older codes was broken.
President Wilson was first made aware of this telegram shortly after United States ambassador Walter Hines Page met with British Foreign Minister Arthur Balfour on the 23rd of February to gather more evidence. The president than waited until the 28th February to release the enraging telegram to the media as he needed details verified from telegraph company files in the US. The telegraph’s story does not end so simply though as it was plagued with public scepticism brought on by claims in newspapers of the Hearst press empire that the telegram was a British forgery designed to bring the US into the war on Britain’s side. This view was supported by the existing anti-British sentiment within German/Irish-American communities as well as pacifist and pro-German lobbies supported by both German and Mexican diplomats. This left the president in an extremely tricky situation as he knew the telegram to be genuine but he could not release the proof without harming the British cryptography operations. Luckily for President Wilson, help was at hand from the most unlikely of sources… the author of the telegram himself. Zimmerman realising that the cat was out of the bag, delivered a speech to the Reichstag on the 29th of March to defend his motives for writing such a threatening telegram. He began his speech by explaining that he had not written a letter to Carranza but rather to the German ambassador via a route that had appeared to him to be a secure one. To defend the threat of the unrestricted submarine offensive, Zimmerman claimed that he had hoped the US would remain neutral and that his instructions to the Mexican government were only to be carried out after the US had declared war. He even went as far as to blame the President for breaking off relations with Germany with extraordinary roughness after the telegram was received which meant that the German ambassador no longer had to opportunity to explain the German attitude.
You can probably guess that the verification of the telegram’s authenticity and the speech itself did not bode well with the American public who did not like the idea of Germany ruthlessly deploying their submarines against any ship bearing the stars and stripes. The deception of German High command enraged the American public enough to rouse support for a 82 to 6 in favour in the senate on a resolution for war on the 6th of April 1917. Where did this leave Mexico in the war? Well the telegram encouraged the US to de jure recognise the Carranza government on the 31st of August to ensure neutrality with its neighbour. Mexico remained so neutral in fact that while Carranza guaranteed that German companies could keep their operations open in Mexico City, Mexico was producing 55 million barrels of oil in 1917 alone and 75% of the fuel used by the British fleet came from this source.
While it can be argued that it was the unrestricted submarine warfare against American merchant ships in the Atlantic which brought the US into the war, 80-90% of the shipping in the Atlantic was being sunk by U-boats months before the declaration of war came. The telegram overruled the desire for US isolation from the European conflicted by providing the American public with the German confession that their neutrality was to be infringed upon but they weren’t to know until it was too late.