Most Americans know that it was the Zimmermann Telegram, sent by Germany to Mexico at the height of World War I, that brought US into the war in Europe. Frustrated with blatant US support of Britain, Germany solicited Mexico to invade the southern United States and offered aid and assistance. However, the telegram was intercepted and decoded by British intelligence and passed to the US, which provided the sufficient casus belli for war.
What few people know is that the Mexican response was, on its face, carefully considered. The country was then undergoing a constitutional crisis shepparded by President Venustiano Carranza, who assigned the military with a feasibility study of a takeover of lost territories of Texas, Arizon, and New Mexico. The study concluded that the plan as proposed by Germany was neither possible nor desirable for the following reasons:
* + Attempting to re-take the former territories would mean certain war with the United States.
* + No matter how “generous” it was, Germany’s “financial support” would be worthless as the United States was the only sizeable arms manufacturer in the Americas.
* + Even if Germany was to supply arms, the British Royal Navy controlled the Atlantic sea lanes, unless if absolute submarine warfare truly was successful in destroying the British fleet, which Mexico doubted.
* + Even if Mexico had the military means to re-take the territory it would have had severe difficulty pacifying the large English-speaking population.
Mexico accordingly provided an offical rejection to the offer by Germany — two weeks after the US declared war on Germany.
Also, I find it interesting that the decoded text of the telegram referred to possible involvement by Japan:
… we propose an alliance on the following basis with Mexico: That we shall make war together and make peace together. We shall give generous financial support, and an understanding on our part that Mexico is to reconquer the lost territory in New Mexico, Texas, and Arizona… suggest that the President, on his own initiative, invite Japan to immediate adherence with this plan; at the same time, offer to mediate between Japan and ourselves.
Reading the text of the telegram was the first I heard of the Japan connection. Interesting to note that the possibility of war between the US and Japan, and peace/alliance between Germany and Japan, was openly discussed at this early year of 1917.