Hi,
If you wish to wonder about history, think about what what might have been (good and bad) if the US had kept all of Mexico after the Mexican War.
When Mexico could not keep order in its own country, Texas rebelled and won its freedom. Then turned to the US for help. Similar with the rest of the southwestern US - the rest was also tied up in manifest destiny.
IIRC, the Southwestern US was PURCHASED by the US after the Mexican War for about the same amount of money that it paid for the Gadsden Purchase (to get a less mountainous way towards California for a railroad). This probably includes Nogales and Tombstone in AZ and Rodeo in NM right along the Mexican boarder. An SP line IIRC.
If Mexico had been part of the US, would Palmer's NdeM have built north of El Paso to meet the D&RG? A north south trunk between Mexico City and Colorado would have helped strengthen ties. Same for the SPdeM (I think that is the Southern Pacific of Mexico that ran south through Nogales).
As for the US "taking" parts of Mexico - hey - if they had been able to keep peace in their own nation, the US would not have gotten involved AND the US did pay for parts we kept (even at a discounted price).
Everyone works on revisionist history.
Oh well.
Doug vV