So if we seize Mexico then are they still illegal aliens?
“So if we seize Mexico then are they still illegal aliens?”
They’d be a conquered people. They can be called anything we wish.
No need to invade right off. Just offer the northern states a choice: continue as you are and risk invasion, or choose annexation on terms similar to those of other US protectorates. Subject to accomplishment of certain milestones, the area may be converted to US territory at a later time with all benefits accorded to US territories.