The southern part of South America is made up of the countries of Uruguay, Paraguay, and Argentina. These three countries are some of the richest nations in South America. All three have large populations of people of European descent, as well as people of mixed European and Indian descent called mestizos.

Some of the most important features of the Southern grassland region are the rivers. Several inland rivers flow into the Rio de la Plata. This is an estuary, or a wide expanse of river that forms where a flooded valley meets the sea. In the southern part of South America, several major rivers flow into the Río de la Plata. Four of these rivers form the boundaries of the countries in the area, including the Uruguay, the Pilcomayo, the Paraguay, and the Paraná. Buenos Aires, the capital of Argentina, and Montevideo, the capital of Uruguay, are located on the Río de la Plata. The mazes of rivers in the Southern grasslands allows people in the region to ship goods effectively and cheaply, helping the economies of these cities and countries.