Ok, well thanks for the responses.
However maybe I was to general,
Lets say the CSA won its independence in 1862-63, I'm guessing the why isn't that important. The CSA wins the New Mexico Territory (or whatever it was called then, lets keep it at Arizona and New Mexico). Afterwords, the Confederacy, seeing the importance of a link to the Pacific for trade and economic expansion, asks for Mexican lands, to which they are promptly declined by Mexico.
The CSA, invades Mexico for land and soon the US joins in, officially to "defend" their southern neighbor from an expansionist "American Empire". And unofficially declaring war to avenge their humiliating defeat. The conflict is in the end, inconclusive, and only a lot of casualties on both sides.
Something I came up with in my head in just a few minutes, doubt it would happen but just something along those lines.
P.S. I am not accounting any European intervention.
Thanks,
How long after the ACW is this rematch over mexico? I'm not convinced that the CSA can win a rematch with the US which would most likely have a more well run and equipped military in the aftermath of a civil war loss. Being that the Confederate congress was very much against a large military budget even during the war, they are going to have a hard time competing with a militarized, and industrialized USA. I know Turtledove seems to think otherwise, but TL-191's second mexican war was largely ASB in my opinion.