Texas is the biggest state with vast resources and self sufficient in food and oil. After securing their backs with Arizona, they need to mount a decisive offensive to annex the other southern states and create a buffer zone against any threat from the north.
Don't forget that with Texas occupied fighting other states, their resources to guard the border with Mexico would be stretched pretty thin. I'm sure the cartels would seize the opportunity to move north. You'd want to protect the border at the same time you're fighting a war, and that would be tough. The same would apply to California to a lesser extent because of a smaller border.
Texas is the biggest state with vast resources and self sufficient in food and oil. After securing their backs with Arizona, they need to mount a decisive offensive to annex the other southern states and create a buffer zone against any threat from the north.
Don't forget that with Texas occupied fighting other states, their resources to guard the border with Mexico would be stretched pretty thin. I'm sure the cartels would seize the opportunity to move north. You'd want to protect the border at the same time you're fighting a war, and that would be tough. The same would apply to California to a lesser extent because of a smaller border.