BTW, there were substantial numbers of Mexicans in (mostly Southern) California, Texas, Arizona and New Mexico, but they fell into two categories: if they were ordinary peasants, they lived an essentially subsistence life not much different than in Mexico. if they were part of the old Spanish/Mexican upper class, they integrated pretty successfully.
In California, for example, the old Spanish/Mexican elite were known as Californios and were often highly respected members of the upper reaches of California society. As a small child in San Francisco, I remember being introduced to one or two of them, very very old women (in their 90s-100s in the early 1950s), as great ladies of California.