An "American Mexico" in WWII

In 1919, there was a major war scare with Mexico over a attack on an American diplomat and a threat to nationalize the oil industry (largely owned by Americans), which came at the worst possible point as America was already in the throes of the First Red Scare; Congress at this time was producing documentation of Pro-German and Pro-Bolshevik actions within Mexico, which served to inflame tensions further. The crisis ultimately reached its decisive point in November, when Secretary of State Robert Lansing sought to issue an ultimatum to force a conflict, with the support of much of Congress. Before he could, however, Wilson recovered sufficiently from his stroke to derail the actions of Lansing and Congress.

For more info:
Woodrow Wilson and the Mexican Interventionist Movement of 1919
1919: William Jenkins, Robert Lansing, and the Mexican Interlude
Tempest in a Teapot? The Mexican-United States Intervention Crisis of 1919

Congressman J.W. Taylor of Tennessee captured the feelings of many:

Said feelings were the culmination of a decade of frustration and anger with Mexico, stretching back into the height of that country's Revolution/Civil War. To quote from "An Enemy Closer to Us than Any European Power": The Impact of Mexico on Texan Public Opinion before World War I by Patrick L. Cox, The Southwestern Historical Quarterly, Jul., 2001, Vol. 105, No. 1 (Jul., 2001), pp. 40-80:

According to Never Wars: The US War Plans to Invade the World by Blaine Pardoe, the basis for what later became War Plan Green was first created at this this time, and was later refined into the aforementioned war plan. From that, we know the general idea was of a force of around ~400,000 U.S. soldiers (Both Army and Marines) being used to fight the conflict, with a holding action and limited offensives along the existing U.S. border in Northern Mexico. The main thrust, however, was to come via an amphibious landing action against Veracruz and from there an overland campaign against Mexico City, with the capture of said location to be the main objective. Essentially, in most ways, it was a replay of the earlier conflict in the 1840s.

So let us say Wilson doesn't recover in time or outright dies; Lansing is able to force through the ultimatum, Mexico refuses and the end result is a Second Mexican American War. The war would probably last a year or so in its conventional phase, ending with the U.S. military seizing Mexico City, inducing the dissolvement of the existing Mexican Government. An insurgency would probably form based around the remnants of the old government and other factions existing within Mexican society, but the U.S. in the first half of the 20th Century had an excellent record against those, winning against both the First Philippine Republic and crushing various insurgencies in Central America as well as the Caribbean.

The terms of the peace, we shall say, involve the U.S. taking Northern Mexico in as a direct annexation while the rump Mexico left has a Pro-U.S. government installed with terms broadly similar to the Platt Amendment that defined U.S. relations with Cuba or the Tydings–McDuffie Act with the Philippines. From thereon, we shall assume the course of history is mostly the same by the the time we reach the WWII-era. By that point, there will have been 20 years of economic and political integration, enabling the U.S. to use Mexico's resources to fight the conflict in a way that was impossible historically.

While I doubt Mexico would offer much in the way of industrial output directly-at least in terms of heavy industry and finished products like tanks, for example-it would probably have light industry (most likely U.S. subsidiaries) that could contribute in a minor capacity. Really, though, the main benefit for the American war effort would be Mexico's human resources. In 1940, Mexico had a population of roughly 20 million which, if it held the same mobilization rate as the United States of 12.7%, would yield about 2,500,000 additional workers/soldiers to the U.S. economy for WWII. Given a divisional slice of ~30,000 per in WWII, I could see this allowing the U.S. to field 130 divisions in the conflict instead of the "90 Division Gamble", while also boosting overall industrial output so as to appropriately equip said divisions.

Finally, one other effect I'm less sure about is the impact on small arms development. Historically one of the main reasons the U.S. stuck with the .30-06 is because of the large surplus stocks from World War I; even then, the .276 Pedersen was the round of choice for what became the M1 Garand. A Second Mexican American War in the early 1920s would help to draw down those stocks faster than historically, which could enable the .276-version of the M1 to survive and become the predominant type. That would allow for a 10 round clip instead of the historical eight, which could later be refined into an M1 Carbine style underside magazine of 15 to 30 rounds. By 1945/1946 the U.S. historically was experimenting with a select fire version of both the M1 Garand and the Carbine, which here I can see happening sooner because of the need to replace the BAR as well as the .276 round making it more viable in the case of the M1.

So, 130 U.S. Divisions and, likely by 1943 or so, said Divisions being equipped with assault rifle M1s.That would definitely have an impact on the course of the war. If there is no landing craft pause in 1942-1943, it's likely Operation Round Up would be viable in 1943. That would fundamentally speed up the end of the War in Europe and likely move the Iron Curtain further East than the Elbe; maybe the Oder or even, possibly, the Vistula?

 

Unless the 276 had a much lighter recoil than the 30.06 had, a full auto Garand would be uncontrollable. I had a Garand with a worn sear that would intermittently go full auto, so I have experience..