1. I don't see why the Aztecs would aid Native Tribes in north america. I think it would be much more likely that the Aztecs would try to conquer those tribes before they aid them. It is not as if the Aztecs have some racial alliance against the White Man.
2. That is if the Aztecs have a long enough reach to even cross those areas.
3. I am pretty sure there are alot of tribes between them and the North American (plain?) tribes that could easily defeat the Aztecs.
http://en.wikipedia.org/wiki/Gaspar_Yanga
4. I would argue with the idea of Succession in an essentially wild landscape. Like what if black slaves in Mexico decided to go maroon and start up a
palenque. This act of rebellion is not quite succession because instead breaking away apart of Spanish territory they instead are founding their own town far off in the jungle. Away from the sovereign territory of Spain. The black slaves elect a King from an African royal house hold and bang a new nation in North America.
Now this occured many times historically, but over time these new entities were reintegrated into New Spain. But this unlike reintegrating the South after the civil war, was dealing with a totally foreign culture and political system (elective monarchy).
Nations in North America I would suggest:
Kingdom of New Mbundu (united slave state with capital of Veracruz)
Holy Kingdom of Deseret (Mormons)
Metis Confederacy (
http://en.wikipedia.org/wiki/Metis_Confederacy)
Osage Nation (oil tycoon natives?)
Seminole Nation (mixed black and native republic of the swamps)
Tecumseh's confederation (napoleon of the North America)