Roy, I do agree there would have been war with Mexico IF the South had won a peace treaty with the US. The Confederates would have supported Maximillian's regime and defeated any hopes of Mexican encroachment.

There are many variables, but assistance from France would surely have prompted the CSA to back Maximillian if it helped then win independence.

Texas had a large problem with Mexico, but also with Commanches and Kiowas. The weak effort of the US Army to protect the frontier would have been abandoned even if Texas had not seceded.