Street Disciple, the US never needs to build Hoover Dam for all the water and electricity in its current form. LA is a minor community of about 50,000 today!
Actually this might have been bad for the South, once committed to an area they had little choice but to stand by a claim(hence Kentucky and Maryland on the CSA flag), on the grounds that reconsidering one secession might weaken them all. Yet the USA would have had every advantage in terms of manpower and of supply. The ability of the CSA to recruit manpower in the southwest would have been virtually non-existant, except a few thousand in California. Remember, the people there voted to be a free state, and went massively for the three union candidates in 1860@90%).
Once involved, the popular mood in California would certainly provide a majority for the USA, not to mention the army forts and Pacific Squadron for support, leaving an outnumbered and outgunned force at the end of a terrifyingly long supply line. Yet a retreat now would have been a disaster for the south. Simply falling a land grab in New Mexico is one thing but losing everything west of Texas would look very bad, no matter how brief the tenancy, perhaps deterring European interest.
And if the Union forces could now open ANOTHER front in western Texas?
The major populations were California(majority free-state), Utah, and Oregon(the latter two overwhelmingly free-state) plus the Navajo. The USA would have had a big edge. Let us also note that Utah in particular would have been an invaluable base. Hmm, another POD, where Utah enters the US thirty years sooner in reward of its loyalty in 1861...
And what would have happened if this DID become a major theater? Most likely an early collapse of the Confederacy, as their ability to provide men, weapons, and gunpowder was all questionable. Supplying a mere 20,000 might have broken the back of the South.
As it was, in OTL, the situation near Richmond was by no means certain for the first year, and the situation in Kentucky/Tennessee bordered on catastrophic. I believe it was A.S. Johnson, an exceptional officer of proven courage, who vowed to avoid and even retreat rather than engage in ANY battle that might be averted, on the grounds he had NO GUNPOWDER!
No doubt less than fully truthful, but if supplying Tennessee was a major problem, Arizona would have been hopeless.
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