Chaco War

Chaco War (1932-35), conflict between Bolivia and Paraguay over the Chaco Boreal, a sparsely populated region to which both countries laid claim. Beginning in 1906, Bolivia began constructing small forts in the Chaco Boreal, inching progressively farther into what Paraguay considered its territory. Paraguay then countered with its own forts and in the 1920s encouraged settlements in the area by Canadian Mennonites to bolster its claims.

Full-scale warfare broke out in 1932. The larger and better-trained Bolivian army initially held the advantage, but the Bolivians, used to a mountain climate, found it difficult to operate in the hot and humid conditions of the Chaco Boreal lowlands. Superior tactics and knowledge of the terrain, combined with fierce fighting, enabled the Paraguayans to gain control of most of the area by 1935. A truce was agreed upon and a final treaty was signed in 1938, giving Paraguay three-fourths of the region and Bolivia the rest. About 50,000 Bolivians and 35,000 Paraguayans died in the war.