PARAGUAY: Yes, that came to mind too. The Paraguayans had a very strong national identity and often fought like fanatics. One thing to consider is that the War of the Triple Alliance against Paraguay was what forged Argentina as a nation rather than a geographic area with autonomous provincial leaders opposing politically and often militarily the attempts of Buenos Aires to centralize power. In addition to rescuing its political allies in the Uruguayan civil war, Paraguay's vague ambitions contemplated things such as trying to win over Corrientes and Entre Rios from Argentina and gaining a corridor across Brazil to the sea, but Lopez dithered a long long time after mobilizing while his Uruguayan allies were crushed with Brazilian troops. In seeking to preserve what he saw as a balance of power in which Paraguay played a balancing role and by needless provocations, he united historical rivals Brazil and Buenos Aires against him.
But there are any number of PODs in this process. Prompt action could have restored his ally in Uruguay and occupied the intervening territory - a deal might have been struck in Corrientes and Entre Rios. This, however, would not fit the racial or nationalist profile you are looking for.
BRAZIL: Emperor Dom Pedro II was wildly popular and admired both at home and abroad, and the coup was a tiny military cabal that had to rely more on guile than force to get the emperor out of the country and set up a military dictatorship. For example, some of the key troops used in the coup were told they were acting against a coup attempt. The Emperor was deceived as well, and was weary of his role so largely acquiesced in the result to his later regret. His daughter was not interested in being Empress, and it was generally admitted there was no suitable successor, so the Empire could run for some more years but a changeover was going to occur and a military coup then then could well have happened. The slaveowners did not like abolition, but would not have considered themselves overthrowing the highly respected Emperor in his lifetime.
Brazil was too multi-racial and multi-ethnic to support a race-based ideology, but maybe you could posit that the order to abolish slavery was not given while the Emperor was on a trip abroad and that a military government developed an ideology around European or Brazilian identity, continued slavery, and an element of Manifest Destiny to the Pacific.
The former Brazilian province of Banda Oriental (Uruguay) would be a logical first step in extending the borders. Bolivia and Peru would be a militarily and logistically more practical route to the Pacific (with an Atlantic-Pacific railway) than Colombia or Ecuador, and less likely to attract united opposition.
Mysticism seems less likely to me than social darwinist and racialist doctrines with Catholicism used to turn back reformists.