The threat of Chile's expansion to the north, together with the constant turmoil in Peru and repeated attempts by Gamarra to invade Bolivia, makes military intervention, by Marshall Andres Santa Cruz, in a Peruvian civil war in 1835, a matter of life and death for Bolivia.

After winning a number of battles in Peru, Santa Cruz reorganizes that country into two autonomous states--Northern Peru and Southern Peru--and joins them with Bolivia in the PeruBolivia Confederation with himself as protector.

The potential power of this confederation arouses the opposition of Argentina and, above all, Chile; both nations declares war on the confederation.