Bolivia–Paraguay border

The Chaco Boreal

After independence Bolivia and Paraguay both claimed the Chaco Boreal, the northern Gran Chaco between the Paraguay and Pilcomayo rivers. Bolivia argued that it had belonged to the colonial Audiencia of Charcas, from which Bolivia was formed; Paraguay said it had held the land continuously since colonial times. Treaties signed in 1879, 1887 and 1894 were never ratified, and later efforts at arbitration and mediation broke down when fighting broke out in 1928.^[1]

From mid-1932 to a ceasefire on 12 June 1935 the two countries fought the Chaco War. A peace treaty signed in Buenos Aires on 21 July 1938 left the boundary to the presidents of six mediating countries, whose award of 10 October 1938 drew the present line: nine straight lines from the Pilcomayo, then the Rio Negro to the Paraguay River. A marker once put on the wrong hill was corrected in 1969, when the real Cerro Chovoreca was found 7.5 km to the north.^[1]

Closing the file

In April 2009, at a ceremony in Buenos Aires, Presidents Evo Morales and Fernando Lugo received the final record of the agreed boundary from Argentina, which chaired the guarantor countries of the 1938 treaty. Morales said the war had been driven by transnational corporations rather than by the two peoples.^[3]

Demarcation went on. In September 2026 a joint commission meeting in La Paz, checking drone surveys against desk data, agreed the last 3.5 km along the Rio Negro. Bolivia said the work had taken 88 years; Paraguay said they would be the only two countries in South America with fully demarcated borders.^[2]

“Bolivia and Paraguay have completed the delineation of their entire international boundary”^[2]