....the Rio de La Plata is downriver from their power base in the Andes, and it's faster to reach Buenos Aires from most of Bolivia than it is to get to say, Lima. I completely disagree; it's the natural expansion of power for the Inca Empire. The jungles are anathema, the Mapuche are annoying and not particularly wealthy, and the Spanish are established to the north. Not to mention, the Spanish explored more of South America as a result of the conquest of the Inca, establishing a settlement which they promptly abandoned, only to try again in 1580 once controlling the mouth of the river became critical to stop smugglers from the Andes avoiding shipping out of Callao. Likewise, the Inca are likely to see the Rio de La Plata as a strategic point of control not unlike the US and New Orleans. Not only are the Inca far closer, able to more easily ship settlers and soldiers than any European power, but they're also likely to see Buenos Aires as the ideal point of contact with Europe; a place to trade where they can easily send their goods downriver, cut out any Spanish middlemen from Panama and Colombia, and isolate Europeans to a single city where they are unlikely to venture into the heartland. I'd expect it to have a notable European population, likely plenty of Portuguese, Dutch, and English, but the Quechua will undoubtedly dominate such a settlement. The majority of Europeans won't be settling down as farmers; maybe their mixed offspring with local Quechua and Charrua will, but not too many. They won't die en masse and require constant replenishment of manpower like in the Indian Ocean and Sub-Saharan Africa, but their numbers are unlikely to be more than a large minority, even in a boomtown scenario.
