The Machain – Irigoyen Treaty was a border treaty signed in Buenos Aires on 3 February 1876 between Paraguay and Argentina. Concluded in the aftermath of the Paraguayan War, it was signed by Facundo Machaín and Bernardo de Irigoyen. That decision created a scandal in Bolivia, which claimed much of the disputed Chaco region. The unresolved conflict would much later lead to the 1932-1935 Chaco War.