Chaco War

From September 1932 to June 1935, Bolivia and Paraguay fought over the Chaco Boreal, the dry, thinly peopled northern part of the Gran Chaco plain, which both claimed and which was believed to hold oil. Nicknamed the "War of Thirst", it was the deadliest war in South America in the twentieth century and an early example of modern machine-gun, armoured and air warfare on the continent. Paraguay, the smaller country, won and kept most of the disputed land.

Both countries had lost territory in nineteenth-century wars. Paraguay had been shorn of much of its claimed land after the Paraguayan War of 1864–1870, and Bolivia had lost its coast to Chile in the War of the Pacific. When the 1929 Treaty of Lima between Chile and Peru ended Bolivian hopes of regaining a Pacific outlet, the Paraguay River, reached across the Chaco, looked like Bolivia's best route to the Atlantic. Bolivia cited colonial boundaries; Paraguay pointed to actual settlement by its ranchers and by Mennonite colonists. Oil discoveries in the Andean foothills raised the stakes. Some writers have argued that Standard Oil and Royal Dutch Shell stood behind the two sides, a view the historian Matthew Hughes found little archival evidence for.

Forts and outposts crept into the disputed zone for decades. Blood was first shed in 1927, and in December 1928 the two armies raided each other's forts before mediation restored the old lines in 1929. Both then began to buy weapons abroad. In June 1932 a Bolivian unit destroyed a Paraguayan fort at Pitiantutá Lake against its president's orders; Paraguay retook the site, and Bolivian President Daniel Salamanca ordered the seizure of further posts, including Boquerón.

Paraguay mobilised quickly under José Félix Estigarribia. Its forces besieged Fortín Boquerón from 9 September 1932 until the garrison of about 600 fell on 29 September. Bolivia, with roughly three times Paraguay's population, then turned to the German general Hans Kundt, who launched a series of costly frontal offensives in 1933. Attacks on Fortín Nanawa in January and July 1933 failed with heavy Bolivian losses, and the initiative passed back to Paraguay.

Estigarribia's troops specialised in marching through the scrub to encircle Bolivian positions. At Campo de Vía in December 1933 some 7,500 Bolivian soldiers surrendered, and Kundt resigned. After a brief ceasefire, the Paraguayans pushed north-west through 1934. In November another two Bolivian divisions were surrounded at El Carmen, a Bolivian cavalry corps disintegrated for lack of water near Yrendagüé, and army officers forced Salamanca from office. Bolivian conscripts, mostly Quechua and Aymara highlanders, suffered badly in the hot lowlands, while their supplies travelled along poor roads; Paraguay could use railways running into the Chaco from its river ports.

In early 1935 the Paraguayans reached the Andean foothills and attacked towards the oilfields around Villa Montes and Camiri, but Bolivian defences held. Exhausted, both sides agreed a ceasefire that took effect at noon on 12 June 1935.

A treaty signed in Buenos Aires in July 1938, with Argentina as the leading mediator, gave Paraguay about three-quarters of the Gran Chaco; Bolivia received river navigation rights. The final border demarcation was signed only in 2009. Estimates of the dead differ: one set of figures gives some 56,000–65,000 Bolivians, about 2% of the population, and about 36,000 Paraguayans, about 3%. Paraguay held around 21,000 Bolivian prisoners. In Bolivia the defeat fuelled the reformist "Chaco Generation" that led to the revolution of 1952. Little oil was found in the Paraguayan Chaco for decades afterwards.

Our 1930 map shows the disputed Chaco on the eve of the war, and the 1938 map shows the region in the year of the peace treaty.