The Restoring Army rearguard led by General Manuel Bulnes successfully held the bridge over the Buin River in the North Peruvian territory from the attack of the Confederacy Army commanded by Marshal Andres de Santa Cruz,[2] yet retreated to San Miguel leaving the field before Santa Cruz could engage him again.

Chile, feeling threatened by Andres de Santa Cruz' growing influence in the continent and his intentions to create a Peru-Bolivian Confederacy, declared war on 1837.

Chile sent an expedition under Manuel Blanco Encalada, but the latter failed in his task, and surrounded and outnumbered at Arequipa was forced to sign the Treaty of Paucarpata on November 17, compromising to resume trade relations with the Confederacy.

The army assembled by Chile for the second expedition was formed by seven infantry battalions, two cavalry regiments, plus six artillery pieces; having a nominal strength of 5,400 men.

[4] Santa Cruz's army was strong in about 6,000 men divided into four Corps, made up by Peruvians and Bolivians, all veterans of internal wars in their respective countries.

This tense situation led to a confrontation and a subsequent engagement at Portada de Guias on August 21, where Bulnes obtains his first victory in this campaign and enters in Peru's capital city.

With the army decimated by deceases, the lack of discipline of the newly added Peruvian troops under Agustin Gamarra, and surrounded and beset by montoneros, a council decides to leave Lima on November 8.

The restoring plan consists in to leave Lima and move north, trying to avoid a direct confrontation with outnumbering Santa Cruz' army.

Once arrived to Huacho on the 13, the sick and the wounded are sent to Trujillo and Piura, along with the poor trained Peruvian soldiers, while the rest of the army are to occupy the Huaylas Corridor, where the chances of gaining tactical advantages are stronger.

The Bolivian Captain Juan Jose Perez with a company of the Cazadores Nº 2 Battalion, threw himself with a few soldiers to the river trying to cross it, but almost all of his men drowned.

This situation continued until January 20, when at Yungay Bulnes defeated decisively the confederate army, vanquishing the Peru Bolivian Confederacy forever.