My point being that Mexico has no claim to any part of southwest US as they say. Then too, it goes back to why don't they speak any of the 63 indigenous languages in Mexico? There still are native Mexicans but then most are direct descendants of Spanish Conquistadors.
Spain settled much of the Southwest and Pacific coast, but Russia had little to do with it; when Lewis & Clark set out to map the “Louisiana Purchase”, Spain sent troops to try to intercept them - Spain had already claimed much of that land, but was unable to settle it in any numbers - their competition (which later became ours) was British claims.
Spain held much of the “American Southwest” until Mexico gained their independence; Mexico then owned the territory, but couldn’t defend it against American designs (Santa Anna of Alamo fame/infamy was in the Spanish army until independence; he then led the new Mexican army). The US doesn’t even dispute this; we paid Mexico for the land we took.
Descendants of conquistadores, or any other other Spaniards, are a very small percentage of Mexico’s population; it is an Indian nation. Some Latin American countries had few or no natives; they are “white” countries today (Argentina, Chile, Uruguay). Others had few Spanish settlers; they are “Indian” countries today (Peru, Ecuador, Honduras). Mexico is undoubtedly one of the latter; Spaniards bear little resemblance to the dark little hobbits filling Mexico and California.