It somehow bothers me it annexed the yucatan peninsula (all the 3 states, and it seems like a bit of Tabasco too) yet it left Chiapas be... Which, IRL, was part of the first UPCA, at least give them los altos, man! Also, IRL yucatan did have one hell of a separatist sentiment, at times it even became defacto its own thing in all but name while Central and northern Mexico were busy with the civil war that popped up every decade or so (19th century Mexico was even messier than you'd think) in Mexico there are even jokes about the "Sister Republic of Yucatan" (referring to the state, not the whole peninsula) and, other than Guatemala and Belize, they don't really have much stronger cultural ties with the rest of CA than they do to the rest of Mexico... so I'd think a but of "civil unrest" would make some sense (also, did Mexico not abolish the viceroyal Casta system in your universe like it did in ours? Because IRL Mexican unrest was mostly along Religious/ideological/linguistic lines, that or Caudillos (basically warlords) viying for personal power