The Chaco War (1932–1935; Spanish: Guerra del Chaco, Guarani: Cháko Ñorairõ) was fought between Bolivia and Paraguay over control of the northern part of the Gran Chaco region (known in Spanish as Chaco Boreal) of South America, which was thought to be rich in oil. It is also referred to as La Guerra de la Sed (Spanish for "The War of Thirst") in literary circles, for being fought in the semi-arid Chaco. It was the bloodiest interstate military conflict fought in South America during the 20th century, between two of its poorest countries, both having previously lost territory to neighbors in 19th-century wars.