Carlotism was the plan of Carlota, Princess of Brazil, to conquer Buenos Aires and Northern Argentina while in exile from Portugal. Could it have succeeded, leading to (if possible) Brazilian Patagonia?
I have my doubts. Brazil, in spite of its immense size, was really a paper tiger. It lacked manpower and equipment to sustain a large war effort, and the occupation vis a vis annexation of the whole La Plata region would demand it. Being seen as a foreign aggression, it might even incite retaliation from the other Viceroyalties of the then collapsing Hispano-America.
Consider that the Cisplatina was a bite already too big to chew, and the fact that even it, with a much reduced geographical area and centers of power and military projection (consisting mostly of Montevideo, Maldonado and Colonia del Sacramento), was freed from later Brazilian occupation, shows that Portuguese America, in spite of its resources, had little to show in warfare, in this period.
I think Carlotta was claiming Spanish South America, most intensely the Vice Royalty of Rio de la Plata, as the rightful Royal because of the mucked up royal situation in Spain, and the alternate Junta system.
She wanted to create a kingdom (Queendom?) with herself at the top, ruling as an absolute monarch. It was not going to be part of Brazil. She was on quite bad terms with hubby Joao, conspiring at times to usurp his rule in Brazil, so I think the idea was to leave him with Brazil while she took Argentina.
At one point, this non existent crown was offered to, or she conspired to, a Bourbon orphan (Pedro Carlos, son of Gabriel, who was Carlotta's uncle - I guess that makes them cousins) who had escaped to Brazil with the Braganza clan). The idea was that he would be the figurehead King, while she ruled as regent. He declined to participate.
There is some speculation that a politically astute Carlotta could have found support for her plans. There was support for a monarchy in Argentina. If a good candidate was available, it might have gained momentum. The problem for Carlotta was that she wanted absolute powers, and there was minimal support for that. Argentinians wanted a big say in gov't with a limited share of the power going to the throne. Thus, her plans were mostly a lot of dreaming, jabbering, and letter writing, with little real chance of becoming reality.
Now, if she had a personality transplant, or Pedro Carlos was more than just a weakling pawn (it was speculated/rumored/slandered that he couldn't handle a vigorous sex session with his wife - Carlotta's daughter - became ill and died. Probably slander, but he wasn't known for good health), it would be interesting to see where things went. Being the Queen/Wife of the regent/King of Brazil, her candidacy roused a lot of suspicion. Pedro Carlos with better health/stronger personality (aka a good candidate) was the nephew of Carlos IV, deposed King of Spain, could have stood a chance of establishing a Kingdom. But, alas, Carlotta was not adroit enough, Pedro Carlos was not man enough, and we're left with an interesting, but unlikely to succeed, chapter in history.
Edit addendum: there was to be no conquering. It was to be her conspiring with Argentinian power figures to create this country.