>>35837
Several wars, and more with Uruguay and Paraguay, as well as times Rio de Janeiro and Buenos Aires were allied. Foreign policy was fully directed towards the Platine region and its borders were contested over decades. They had already been relatively fluid in colonial times, when some wars also took place. It's the only densely populated border region between Hispanophone and Lusophone America, easy to access by its rivers and flat terrain and economically valuable because of the same rivers. In that respect it's like the Volga or Mississipi-Missouri.

>>35836
>they turned against the leftist President, because they felt he tries to push them out of power, while they were now quite used to exercising it
They weren't in power in the first place, military crises in 1945-1961 were just attempts to replace one civilian regime with another. The rebels were concerned about the military's institutional decay but were just as politicized as the leftists, and both wanted to use their power to preserve a regime or discard it for another. It was expected, and many of the rebels wished for, that a coup d'état would just get rid of Goulart and renew the civilian political leadership.
Political divisions in the military mirrored those among civilians, so first those must be described.
The existing democratic order was established after the ouster of Vargas after WWII. His opponents gathered in the National Democratic Union (UDN), which was a big tent but after leftists moved away it became right-wing. UDN favored alignment with America, laissez-faire economics and foreign investment. In turn, the Varguist base went to Labor (PTB) and the Social Democrats (PSD). PSD was formed from the former regime's elites and their electoral base in each state. It was thus moderate and tied to power. It wanted to develop the country through mass investment in public works, disregarding inflation, and accepted foreign capital. PTB was based on trade unions and militants. It was similar to the PSD but rejected foreign capital and, by 1964, embraced radical social measures such as land reform. Their positions after 1964 are easy to discern as existing parties were disbanded and replaced with just two, the ruling Arena and oppositionist MDB; most of the UDN and PSD migrated to Arena, and most of PTB to MDB.
Communists were few but had a lot of ties among trade unions and the like. The main pro-Soviet wing wanted to achieve their means through cooperation with the existing order. Among farmers they controlled ULTAB and used to be allied with the much better-known Peasant Leagues, but the latter got in bad terms as by the 60s they had grown too radicalized, had Cuban ties and wanted land reform by law or by force.