While waiting for further answers, you might be interested in previous answers on the subject.

There's an FAQ section, "Post-Independence Fragmentation of Latin America" (in the app, it doesn't obey the "#" anchor, so find the section near the bottom). The basics are covered in the first two, "Why is there not one united nation across all of Latin America?" by /u/LegendaryTubaHero , and "Why did North America split into 3 countries and South America split into 15 though they were colonized similarly?" by /u/Yodatsracist . The other two articles are worthwhile as well, giving other details and discussion.

For Brazil, I think this is good: "Why did the Portuguese colonies in South America evolve into a single country (Brazil) whereas the continent's Spanish colonies broke off into nearly a dozen countries?" , answers by /u/hivemind_disruptor and to-be-determined . They were pointed to by AD1337 in this posting about disruptions of Brazil: "Brazil is a huge country. One could easily imagine that over the course of time it would have splintered into 2, 3, or five different countries. What has kept it together?"

This is not to discourage discussion; the rules expressly permit questions that have been asked before