So, Río de la Plata Basin is 1.2 million square mile area in South America. It is a Humid Sub Tropical Climate by Koppen’s definition, has good soil, and is interconnected by rivers which eventually drain into the ocean. It has almost everything a civilization needs to emerge with a huge population, that could likely dominate most of South America.
In the original timeline, it wasn’t settled very thoroughly by Europeans until relatively late after the Natives were devastated by disease, but much of it still ended ended up being some of the wealthiest and more populous areas of Latin America.
So some questions I have are...
1: What is the likely carrying capacity of the region with pre industrial technology?
2: Could it have become a Native American China or India with early PoD?
3: Why did it take so long for the area to get a larger European population?
4: Are there any TLs where a power based out of there becomes a Super Power?