The Gran Chaco (Quechua chaqu, "hunting land"), dubbed by some as "the last South American frontier", is a sparsely populated, hot and semi-arid lowland region of the Río de la Plata basin, divided between Bolivia, Paraguay, Argentina and a small portion in Brazil called Mato Grosso. It is about 647,500 square kilometres in size, though estimates differ, and located west of the Paraguay River and east of the Andes in Paraguay, Bolivia, and Argentina. It stretches from about 17° to 33° South latitude and between 65° and 60° West longitude, though estimates differ in this case too. Closer to the mountains in the west, the Alto Chaco, is very dry and sparsely vegetated, but going eastward to the Bajo Chaco one encounters lots of thornbrush jungle with quebracho trees and grassy clearings with a wealth of insects. The landscape is mostly flat and slopes at a 0.04 degree gradient to the east.

Mennonites came into the Paraguayan part of the region from Canada in the 1920s; more came from the USSR in the 1930s, and even more from the USSR after World War II. They created some of the largest population centers in the Gran Chaco.