What if Mexico had joined the Confederacy in the Civil War?

Answer 1

That possibility never entered the minds of politicians or the military leadership. It was a foregone conclusion at the outset that the Mexican population, industrial capacity, economy as well as the battlefield capability and leadership would be no match against the US. It is quite unlikely that even the most optimistic military minds in Mexico wasted any time considering that option. It was only a matter of time.

However, if Mexico had won, California would be part of Mexico or an independent nation. The US might not have absorbed Washington and Oregon, which might be part of Canada. Probably New Mexico, Arizona and parts of Colorado would be part of Mexico. The Texas border would be 100 mile further north and Texas might have eventually left the union and absorbed New Mexico, Arizona, Colorado, etc. All pure speculation, of course, and others may reach different but equally valid conclusions.

Answer 2

It was almost impossible for Spain to win such war, as the Latin America's independence movement began when Spain had become such a decadent empire, that it had to defend itself against Napoleonic forces during the Peninsular Wars (1807-1814).

If Spain had won such war, a few years later the United States would have seen the opportunity to fulfil its Manifest Destiny, acquiring all the territories within California and Texas, and possibly present-day northern Mexico as well. It would not have taken all the country, due to a high presence of Native Americans and mestizos in central and southern Mexico, who were deemed as "undesirables" by Manifest Destiny believers and pro-slave interests alike.

It is also likely that England would have taken hold of Spain's weakness to further divide Mexico; it was already owner of a small territory east of Mexico ("British Honduras", nowadays Belize) and would have tried to take over the Yucatan Peninsula and possibly Guatemala as well.

The end result would be a smaller Mexico with more British and/or American influence over the country.

Answer 3

If the French had succeeded conquering Mexico, by helping the Confederates win during the Civil War, most probably the United States would have become several fragmented nations, including the Northern states, California, Texas and one or several groups of nations from the South due to the dysfunctional relation between the member states of the Confederacy.

This would have eventually changed the face of the world, as for example, the United States wouldn't have been involved in WWI, Mexico (being a French protectorate) would have had a good chance of recovering New Mexico and Arizona, and without the help of the North, California would have had to fight alone against Japan during WWII.