On June 10, 1935, in a truce mediated by the Argentinean government, Paraguay and Bolivia agreed to end the Chaco War.
Background During the 1930s, Paraguay and Bolivia went to war for possession of the North Chaco, a dry, forbidding expanse of scrub and forest that lay between the two countries. The North Chaco forms a part of the larger Gran Chaco Plains, a vast region that extends into northern Argentina, western Paraguay, eastern Bolivia, and a small section in western Brazil.
During the colonial era, the Gran Chaco Plains was administered by the Spanish government as a separate territory. In the early 1800s, the Gran Chaco Plains became disputed territory when the South American countries surrounding it gained their independences. The delineation of the borders around the Gran Chaco Plains was not pursued actively, however, because of the region’s harsh climate and the mistaken belief that it contained few natural resources.
Through conquest from wars later in the 1800s, many areas of the Gran Chaco Plains were annexed by the victorious countries. Eventually, what remained undecided was the North Chaco, the region straddling Paraguay and Bolivia and located west of the Paraguay River and north of the Pilcomayo River.
War Fighting broke out in June 1932 with the Paraguayan forces soon taking the initiative. But by March 1935, their offensive had sputtered. Thereafter, the Paraguayan Army realized that while it had achieved its military objectives in the North Chaco, it could not go any further into Bolivia without incurring heavy losses.
While some politicians on both sides demanded for the continuation of the war, the governments of Paraguay and Bolivia were alarmed that the huge human and economic tolls were bringing their countries to ruin. War casualties had reached 100,000 dead, with nearly 60% of that figure suffered by Bolivia. On June 10, 1935, in a truce mediated by the Argentinean government, Paraguay and Bolivia agreed to end the war.
Aftermath The territorial issue of the North Chaco was brought before an arbitration panel consisting of members from South American countries. In its decision, the arbitration panel awarded 75% of the North Chaco to Paraguay, and the rest (25%) to Bolivia. The panel’s decision also stipulated that Paraguay must grant Bolivia access to the Paraguay River, as well as to specified ports and rail facilities inside Paraguay. (Excerpts taken from Wars of the 20th Century: Volume 1.)