Dom Pedro II was never crowned emperor of Brazil, since the country dissolved de facto on 15 January 1843, almost one year before he turned 18.
Instead, he became emperor of Rio de Janeiro and Espírito Santo, the only two provinces that remained loyal to the House of Braganza. He was a constitutional monarch, with the actual leader being Nicolau de Campos Vergueiro, who faced a naval blockade from Britain and was forced to abolish the slave trade.
The strongest countries that arose out of the dissolved Brazil were São Paulo, Minas Gerais, Rio Grande do Sul and Bahia, the first two ruled by Rafael Tobias de Aguiar and Teófilo Ottoni, respectively, both classical liberals who priorized the interests of planters born in Brazil. Tobias de Aguiar was married to Domitila de Castro, the infamous mistress of Dom Pedro I, who thus became First Lady.
Bento Gonçalves remained the president of Rio Grande do Sul until his death in 1847, creating a national bank, unicameral legislature, national constitution (which set up a presidential authoritarian system, even with the superficial similarity to the US Constitution), and merchant fleet based on the Lagoa dos Patos. He also obtained international recognition for Rio Grande do Sul, and got the backing of Britain and France against Rosas. High tariffs on foreign products were maintained. Gonçalves died on 18 July 1847, and was succeeded by Antônio de Sousa Neto, who ruled until 1866 and built the first railways and telegraph lines in Rio Grande, while continuing the protectionist policies of his predecessor.
After Rio Grande do Sul became independent, it faced a streak of autocratic rule that lasted, with a few breaks, until 1921, when Borges de Medeiros, successor to Júlio de Castilhos, was overthrown in a revolution and fled into exile in São Paulo. That same year, Raul Pilla was elected President for the Liberator Party, which advocated for classical liberalism and congressional over presidential prerrogatives.
Rio Grande do Sul had its independence recognized by the United Kingdom, France and Portugal in October 1842.
The newly independent republic soon sided with the two strongest countries of the time against Rosas, importing muskets and gunpowder from them and building a navy of 38 warships with British assistance.
After Antônio de Sousa Neto became President of Rio Grande do Sul in 1847, he continued the schemes of modernisation and protectionism began by Bento Gonçalves, abolishing slavery without reparations in 1850, remodeling the postal service and customs office, building an arsenal in Pelotas that produced firearms and artillery, and building an opera and a theatre. Those reforms made Rio Grande do Sul significantly stronger, and were feared by Rosas, who felt they could spread to the rest of the Platine region. Rio Grande do Sul's annexation of the Juliana Republic in 1850 helped increase tensions in the region.
The army of Rio Grande do Sul was as large as that of the Argentine Confederacy at the start of the war, and the officers had experience from the Ragamuffin War, but the country lacked enough resources and industry to adequately equip it, and its reserves of gunpowder were smaller. This contributed to the defeat at Caseros, which was the beginning of the Allies' defeat.
After the battle, Rosas's hopes of a decisive victory went unfulfilled, and the war became a stalemate that ended with the Treaty of Cordoba. The nonaggression pact was repeatedly broken by both sides, and Rosas remained heavily unpopular; in 1855, a coalition led by Corrientes and Entre Rios overthrew the longtime dictator, and over time, Argentina became the strongest power in Latin America, due to Brazil being split.
As Oribe's health weakened, the Blanco faction, which was surrounded from all sides, continuously lost ground, and he eventually surrendered to the Allies in June, substantially damaging Rosas' cause.
During the following two months, the Allies marched through Buenos Aires province, facing weak resistance, causing Rosas to go into exile two weeks after his army was crushed on 30 July.
Paraguay under Carlos Antonio Lopez remained neutral in the conflict, but aligned itself with the Allies, while the rest of Brazil was not involved at all.
Bartolomé Mitre would eventually emerge as the ruler of most of Argentina, defeating Urquiza, while the rapidly developing Paraguay remained under the rule of the Lopez family until Francisco Solano Lopez died in 1883 and another dictator took over.
López built one of the best-trained but ill-equipped armies in the region, which was successful against the sparsely populated Mato Grosso but not the wealthy and dense São Paulo.
São Paulo politics were dominated by classical liberal planters who made the presidency a mostly ceremonial office, as themselves controlled the government. Statesmen such as Joaquim José de Sousa Breves, the "King of Coffee", and Francisco Peixoto de Lacerda Werneck are more well-known than the presidents of this era.
During peacetime, the Republic of São Paulo relied on the Public Force paramilitary, with the army being small; it was only expanded after López invaded Mato Grosso, defeated it within three months and made it a puppet state after annexing one third of its territory. The Army of São Paulo obtained modern weapons, including Congreve rockets, from Britain and France, who opposed Paraguay's expansionist ambitions.
On 16 September 1867, Paraguay invaded São Paulo in order to obtain acess to the port of Santos, and its army soon captured much of the Comarca do Paraná. The few actual enemy units in the region surrendered, and a Paulista counteroffensive failed, leading to a war of attrition with alternating fortunes until January 1869, when Rio Grande do Sul declared war on Paraguay and inflicted a series of defeats on its forces, leading to Solano López ceding several territories and restoring the independence of Mato Grosso.
After the war, he faced several challenges to his power, from hardliners who saw his use of diplomacy as treason, but violently crushed them, and continued to develop the Paraguayan economy, which was one of the most advanced in Latin America. Relations with neighboring states remained tense, and there were several border clashes with Argentina and Rio Grande do Sul, both of whom continued to distrust López. However, he continued to play off various factions and countries in the region against each other until his death in 1885, whereupon his son Juan Francisco, nicknamed "Panchito" succeeded him.
Juan Francisco proved to be an inept and corrupt ruler who was overthrown in a revolution in 1888. Bernardino Caballero became the dictator of Paraguay until his death in 1912, dismantling the state-controlled economy the country had until
Since the early-to-mid 19th century, Uruguay had faced political turmoil between the Blanco and Colorado parties, and during the 1880s, there were widespread border raids into Rio Grande do Sul.
The Riograndense public increasingly called for the country's government to take an intervention, and, shortly after taking office after the death of a former dictator, President Venâncio Aires, who was a former journalist instead of a military officer, ordered an invasion, backed by the Riograndense fleet of avisos and gunboats, which blockaded Montevideo and prevented British aid from arriving.
By early August 1885, only Montevideo and its outskirts had not been captured, and when the city came under a full-scale assault, the Colorado administration surrendered, bringing Uruguay into the Riograndense orbit until the 1930s, when it began following an independent course.
In 1890, Aires died and Júlio de Castilhos succeeded him. The Castilhistas, as Castilhos' followers were called, largely dominated Riograndense politics until the 1960s, when Leonel Brizola became a left-wing dictator and the last in the country's history as of 2024.