Bolivia in 1841 was hardly a functioning state. The Peru-Bolivian Confederation had recently collapsed, and three separate governments claimed authority over the country. In Chuquisaca, Jose Mariano Serrano headed the legitimate government. In Cochabamba, Jose Miguel de Velasco ran a rival administration. In La Paz, Jose Ballivian had proclaimed himself president. The country was fragmented, leaderless in any unified sense, and vulnerable -- precisely the condition that tempted Gamarra to invade. The Peruvian president had long favored a union between Peru and Bolivia, but only on his terms: Peru dominant, Bolivia subordinate. The political chaos across the border provided the pretext he needed. What Gamarra underestimated was the effect a foreign invasion would have on Bolivian factionalism. Faced with Peruvian troops crossing the border, the three rival governments did something unprecedented: they united under Ballivian and combined their forces.

The armies met near Viacha, a town on the altiplano roughly thirty kilometers from La Paz, at an elevation where the thin air punishes any physical exertion. Details of the battle itself are sparse in the historical record -- what survives is the outcome and its shock. The Bolivian forces, fighting on home ground at altitude they were accustomed to, repelled the Peruvian invasion decisively. Gamarra was killed in the fighting, a rare occurrence in nineteenth-century South American warfare where presidents led from behind the lines. His death sent the Peruvian army into retreat and plunged Lima into political chaos. Vice President Manuel Menendez struggled to maintain authority before being deposed by Juan Crisostomo Torrico. The Bolivian victory at Ingavi was total in one critical sense: it was the last time Peru ever attempted to seize control of Bolivia by military force.

Ingavi settled the question of Bolivian sovereignty, but it did not end the war. Emboldened by their victory, Bolivian forces crossed into southern Peru and occupied Tacna, Arica, and Tarapaca. The occupation, however, proved impossible to sustain. Bolivia lacked the troop strength to hold foreign territory across such distances at such altitudes. In Tarapaca, Peruvian montoneros -- irregular militia fighters -- led by Major Juan Buendia defeated a Bolivian detachment on 7 January 1842, killing Colonel Jose Maria Garcia. In Arica, Peruvian militias expelled the Bolivian occupiers from the port. The battles of Motoni and Orurillo pushed the remaining Bolivian forces back across the border. By February 1842, the overextension was complete, and Bolivia withdrew to its own territory. The pattern was instructive: Bolivia could defend itself brilliantly but could not project power beyond its borders. The altiplano gave defensive advantages that vanished on offense.

Ingavi entered Bolivian national mythology immediately. November 18 became a day of commemoration, and Ballivian became a national hero -- the man who unified a shattered country and defeated an invading president. The battle demonstrated something that Bolivia's fractious political life had not yet proven: that the idea of Bolivia as a sovereign nation was strong enough to override internal divisions when the alternative was absorption by a neighbor. For Peru, Gamarra's death on the altiplano closed the chapter on annexation. The two countries would fight no more wars against each other. The plain near Viacha where the battle took place sits on the high altiplano at roughly 3,800 meters, windswept and largely unmarked by the event that occurred there. The landscape gives nothing away -- flat grassland stretching to the mountains, indifferent to the history it witnessed.