Chaco War Ceasefire (1935)
A ceasefire is negotiated between Bolivia and Paraguay, ending the Chaco War.
Background
The Gran Chaco is a vast, arid lowland region in the heart of South America, long disputed between Bolivia and Paraguay. In the late 1920s, geologists speculated — incorrectly, as it turned out — that the Chaco contained enormous oil reserves, making control of the region strategically vital to landlocked Bolivia, which had already lost its Pacific coastline to Chile in an earlier war. In 1932, following years of skirmishing, Bolivia launched a major offensive, starting the Chaco War. The conflict became the bloodiest war in 20th-century South America.
Did You Know?
Bolivia entered the Chaco War with a larger, better-equipped army trained by German advisors, yet Paraguay ultimately won most of the disputed territory. Much of Bolivia's disadvantage came from deploying troops from high-altitude Andean regions to the hot, waterless Chaco lowlands — a brutal transition that killed nearly as many soldiers through disease and dehydration as direct combat.
The Ceasefire
After three years of brutal fighting, both nations were exhausted. Paraguay had advanced deep into Bolivian-claimed territory, while Bolivia had suffered enormous casualties. Mediated by Argentina, Brazil, Chile, Peru, Uruguay, and the United States, a ceasefire took effect on June 12, 1935. By that point, approximately 57,000 Bolivian soldiers and 36,000 Paraguayan soldiers had died — out of a combined force of some 300,000 — making the war proportionally devastating for both nations.
Aftermath & Legacy
The June 1935 ceasefire ended the fighting, but a formal peace treaty was not signed until July 1938. Paraguay was recognized as holding about three-quarters of the disputed Chaco territory. Bolivia retained access to the Paraguay River and a small port. Later oil exploration confirmed the main reserves lay on the Bolivian side of the final boundary — a bitter irony. In Bolivia the war triggered a series of coups and eventually a 1952 social revolution; in Paraguay it produced a generation of war heroes who shaped the country's politics for decades.