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?