In 2032, major population centers (such as Rio de Janeiro and São Paulo) and industrial centers were targeted by American nuclear weapons , though the countryside from major manufactures and factories being destroyed or abandoned. Much of the Amazon, Cerrado and their wildlife were destroyed by desperate refugees fleeing from the chaos of the urban areas. The resulting famine was felt by the entire nation, which in turn decimated the population.
The government effectively abandoned most of the nation, fleeing deep inland to bunkers, remote towns and areas with naturally formed defenses. The scattered groups of government and military were very isolated from each other, radio communication between these enclaves was very minimal and they only ever ventured out of the safety of their fortifications to scavenge for supplies. However, many of these positions were overrun by bandits or desperate refugees. Sometimes it'd be the military within the enclaves themselves who would mutiny.
However, there always are exceptions and in this case it were the cities of Manaus, Gramado and Florianópolis which were each made victim to single nuclear missiles that detonated prematurely in the air, resulting in a massive (yet smaller than expected) amount of casualties. Many buildings, however, survived the nuclear detonation with minimal damage. The electric grid was taken down but the facilities vital to running it could still be operational due to a variety of fail-safe mechanisms. This was also the case for many things such as the subway, sewage, and water systems. The government sealed off and fortified vital sections of the cities, and these safe zones became home to a few select individuals who possessed skills that were considered vital (such as doctors, government workers, engineers, renowned professors and researchers, along with retired or reserve soldiers) with their families, while those without relevant skills were given an apology and sent away, left to fend for themselves among the bandits and scavengers of the cities - or in other independent communities.
Life in these safe zones was harsh, and the period in which they existed was considered by many as a new military dictatorship: weapons, medicine and food were confiscated and rationed by the government; many sick and elderly died; crime was treated severely and punished either by death or exile from the safe zone. Nearly all the food consisted of vegetables grown in greenhouses. Money became nearly useless, and everyone was forced into closely guarded tenements or repurposed buildings. Private ownership of vehicles was also temporarily banned over fuel concerns and the working age was lowered to from 16 to 14. Re-education programs were undertaken and the previously mentioned skills of the select individuals who were allowed into the safe zones were entually all of the three cities had been retaken within a period spanning 7 years and with minimal casualties.
It followed in the mid 2040's that the nuclear cloud cover and the winter it had brought about started to lift, and expeditions lead by the former military of Brazil were sent past the safe zones and into the countryside. People waited for many weeks for these expeditions to return, and when they did, celebration and festivities returned to the streets after a very long time as they had discovered that crops could grow again and most of the radiation in the southern and central regions had cleared out. After this discovery, a series of concentrated military efforts were made to reclaim the countryside surrounding the safe zones - these operations abandoned the careful tone of past missions and casualties mounted, but the missions were ultimately successful and the land around them along with some rural villages and other small communities were reclaimed within a few months. Agriculture began again and food rationing was gradually phased out in favor of a free market as farmers sold their produce and the government started printing new money and establishing salaries for work. Population began to boom and the scattered military and government officials abandoned their holdfasts and flocked to the newly reclaimed capital of Brazil - Brasília - along with many civilians.
During this time, however, reports began to surface of farmers going missing, civilian expeditions into the jungles never returning, and of savages devoid of all reason attacking and cannibalizing people in the countryside. These reports were often overlooked as rumors by the government, but many people did claim to see large groups of armed men in military fatigues entering the jungles afterwards. No official explanation was given for these men but it is known that after many months they emerged from the jungle and the reports of the attacks seemed to stop. Most of those who originally spread the rumors have since been arrested for various reasons, or have simply vanished. It never truly was confirmed what these rumors and reports may or may not have been, but theories of ACMF experimentation with their own version of RAD-8 within the Amazon have surfaced. The government has denied all access to information regarding these incidents. What is known, however, is that these stories have been passed down from generation to generation, warning of the dangers of the post-nuclear world and the unknown.
In 2058 the "post-flash dictatorship" had ended and large portions of Brazil had been reclaimed - including the coast. Rationing had stopped completely, factories began to work again and cars were back on the streets of some places. Trade with towns and cities of previously neighboring countries such as Argentina began and many towns had electricity. Abandoned bunkers, military camps, airfields and oil platforms were retaken, pre-war military vehicles and equipment were re-introduced to the army - along with newly manufactured models - and many towns welcomed the government forces and joined the Brazilian Republic, most were happy to see the return of law and order, some were simply scared to go head to head with government forces. Few areas which were under control of hostile "factions" refused but after a short skirmish they were taken.
During the mid 2050s, the Brazilian military was reformed and renamed the Maior Exército Brasileiro (MEB). The group which had formerly represented a well armed militia had been given standardized equipment and uniforms, a proper salary, pre-war length training periods and the possibility of Latin-American foreigners to enlist - this was primarily served as a response by the Brazilian government to deal with all the undocumented refugees flooding the streets. The idea being that it'd be preferable for a refugee unfamiliar with law, the Portuguese language and civilization to go through training and be drilled and disciplined before being released back into the public, hence the addition of the word "Maior" (greater or bigger) to the full name of the army forces as the soldiers were no longer only Brazilian - part of them hailing from other South American nations. This practice, however, stopped in the late 70's.
By 2071, nearly all of Brazil was reclaimed and international trade resumed: cargo ships returned to the seas and sailed to places such as the US, Europe, and Eastern Asia. As many of Brazil's old neighbors came to it seeking help to reclaim and rebuild their nations, MERCOSUR was reformed as more of a military alliance and the Brazilian Republic agreed to help it's neighbors in exchange, member states which included Colombia, Venezuela, Ecuador, along with a few other new nations in the Northern tip of the continent were to supply and fund the MEB and were to give Brazilian companies access to their nation's natural resources as well as maintaining a very low tax on trade.
A few years following the reform of MERCOSUR, the La Gran Unión del río Plata (The Great Plate River Union, in English) came into existence, more commonly known by the acronym "URP" consisting of lands in the Southern and Western parts of the continent (Argentina, Bolivia, Chile, and Peru). Although it was very clear that the URP was meant to rival MERCOSUR, the two cooperated with each other in a brief war against a faction in Paraguay that attempted to wrest control of the Itaipu dam in 2079 - a conflict known as the Second Plate River War. The land was partitioned between the two (URP and BR), existing as an autonomous region within the Brazilian Republic. The following years saw a decline in relations however as several border disputes and the growing economic and military power of the URP threatened the status of MERCOSUR as a regional power, and as a result Brazilian ports impounded URP cargo ships headed for North America and were sent back home, the situation nearly escalating to war several times and resulting in increased militarization from both sides. However, since 2105, tensions between the two unions have been decreasing due to Brazil allowing minor participation of the URP's nations in economic decisions regarding MERCOSUR's other countries, along with the end of URP cargo ships' impoundments.
By 2103, many of the MERCOSUR nations had reformed and controlled much of their pre-war territory - many of the member states had a small MEB presence within their borders; Panama had joined the alliance and its canal was rebuilt, allowing for even more trade possibilities. However, the alliance had long ago turned into a puppet of Brazil; many member states were grossly underdeveloped compared to the Brazilian Republic, which thrived; only Brazil enjoyed the low tax rates on trade while most of other nations were barely able to break even due to the taxation and tariffs. The Republic's companies essentially had complete control over the natural resources of MERCOSUR nations. The Brazilian trade fleet had grown to impressive heights and brought in tons of money for Brazil, which it's 'allies' would barely ever get to benefit from. Many of the citizens of other MERCOSUR countries simply enlisted in the MEB during the 60's and 70's or moved to Brazil to escape the grinding poverty of their motherlands, and most of these new soldiers were sent abroad to protect traders and interests that had begun to develop abroad.
When the mysterious Atlanta Crisis occurred, the Brazilian Republic (along with most of the URP's nations) pledged full support to the newly-founded PRT. The current president André Neviso even stated it a "God given duty for Brazil and its allies, with the help of their friends in the North and the West to end the corrupt regime that had brought the world to its knees." MEB troops were deployed to PRT lands, staying away from the front lines and active combat. They fought when the need arose, but mainly act in a support role to the CDF - escorting supply caravans and clearing out bandits to allow for more effective CDF operations. One of the most notable things the Brazilian Republic has done in this war however is establish an embargo between the RCO and PRT, and sinking British ships unfortunate enough to sail near the southern coast of the continental US, which has cause the RCO to pledge support to the US and declared war on both the PRT and the BR.
Brazil was considered a comparatively minor target in the ACMF-NATO nuclear war but was nonetheless made victim to a few nuclear attacks. Compared to other countries at the time, the country recovered relatively quickly once the decade-long nuclear winter that covered the planet lifted, and have since managed to rebuild themselves as a major military and economic power. The Brazilian Republic has re-industrialized very quickly and has become wealthier than its neighbors thanks to international trade with much of the post-nuclear world.
The MEB was formed in the 2050s when the Brazilian military opened it's ranks to soldiers from neighboring countries after the need for a large army to hold and secure the nation's territory and borders against the many threats this new world brought about was realized, Brazil itself being unable to support such a force due to a large population decline following the nuclear war. The BR has stopped this practice during the late 70's due to the steadily increasing population and the comparatively more peaceful state the country exists in. The MEB itself is well equipped and trained, selling much of it's outdated or old equipment to the PRT which they have since pledged full support to following the mysterious Atlanta Crisis.