Chaco War at English => English (The Britannica Concise) Of Explained:
Costly conflict between Bolivia and Paraguay over possession of the Chaco, a wilderness region thought to contain oil reserves. Bolivia, landlocked since the War of the Pacific, was motivated as well by the need to gain access to the Atlantic coast through the Rí o de la Plata system. The war cost about 100,000 lives and so seriously disrupted Bolivia's economy that its deprived masses demanded reform. In a treaty arranged by neighboring countries and the U.S., Bolivia was given a corridor to the Paraguay River and a port, but Paraguay gained clear title to most of the disputed region.