Realism of US client states following the Mexican American war

In my timeline, the Mexican American still occurs, but is longer and harsher; resulting in a harsher treaty.

Originally I had the US additionally annex the states of Sonora, Sinaloa, Durango, Chihuahua, Coahuila, Nuevo Leon and Tamaulipas, but I feel this is way over done. My current Idea is that instead of annexing these states, the US establishes client states to both weaken Mexico and act as buffers.

So instead of annex these areas, the US creates two [maybe three] client states; the Republic of the Rio Grande, the Confederation of North Mexican States [Sonora, Sinaloa, Durango and Chihuahua] and maybe the establishing the Republic of California, only taking Nuevo Mexico and modern Texas for themselves.

Before I explore this idea further however, I could use some feedback. Are these client states realistic and Is the idea of a US supported Independent California ridiculous?
 
The Mexican client states seem plausible. As for California it could maybe work if the Bear Flag Revolt lasts longer and California spends more time separate from the USA. I find it likely that California would eventually be annexed into the US unless it creates a separate national identity and culture.
 
America would want San Francisco Bay, period - it was trying to purchase it since the 1830s. So a client state California Republic will have to contain California below the 37th parallel north and Baja California. It would be and probably remain much more Hispanic than TTL American California, since most Anglos settled on SF Bay pre-Mexican War and the Central Valley post-Gold Rush, and the bulk of the Californios were in SoCal/TTL *California client state.

Funnily enough, New Mexico pondered on declaring independence under the name Republica Mexicana del Norte, probably you can see the northwestern states take that name.
 
What I would say about this is that it doesn't really follow the pattern of US expansion, really until the American-Spanish War.
 
The US would almost certainly take California directly. As Umbric Man points out they had tried to buy it previously.

I can see the US creating buffer states as you said but I think that they could very possibly be annexed at a later date as US business interests and citizens invest in these semi-colonies. After all as client states the US would have a vested interest in their stability.
 

Philip

Donor
As stated above, northern California will be absorbed by the US. It is hard for me see the US not taking southern California and the territories of the Gadsden purchase. They are needed for a southern rail line.

At the time of the OTL Mexican American War, I don't see the need for client buffers. The US just marched into Mexico's capital with relative ease.

Splitting off the northern tier of OTL Mexican states into a two or three clients makes some sense latter on, especially if there is a second Mexican war. Maybe like a Mexican attempt to reclaim territory in the later 1800s. The war opens with a rapid invasion that cuts the southern rail line. The US eventually pushes the invasion back and then establishes the clients.
 
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