The conflict began when Ecuador attempted to sell Amazon basin land claimed by Peru in order to settle a debt with British creditors.

By late 1859, control of Ecuador was consolidated between General Guillermo Franco, in the city of Guayaquil, and a provisional government in Quito headed by Gabriel García Moreno.

Peruvian President Ramón Castilla sailed to Guayaquil with several thousand soldiers in October 1859, and negotiated the Treaty of Mapasingue with General Franco in January 1860.

No fighting took place between the troops of the two countries within the duration of the dispute after the occupation, although a detachment of Peruvian forces pledged by Castilla in the Treaty of Mapasingue was involved in the later Battle of Guayaquil.

Because of the poor geographical knowledge of the area at the time, colonial-era administrations were separated by borders defined with little accuracy via a multitude of Real Cédulas (royal decrees issued by the Spanish Crown).

[10] Peru continued to stand by its position of uti possidetis of 1810, and brought its case before the governments of the United States and Great Britain, which distanced themselves from the dispute.

On July 30, Cavero wrote to the Chancery of Lima, detailing what he considered multiple transgressions carried out by the Ecuadorian government and press against Peru's honor.

[14][15] While the Peruvian view is that Cavero was justified in any means necessary to achieve the repatriation of the territories, his tactics have been called tactless and belligerent by later scholars, and were contrary to his instructions from Lima and detrimental to his goals.

[4] In a law enacted on October 26, 1858, the Peruvian Congress authorized President Ramón Castilla to command an army against Ecuador if necessary to secure the national territory against its sale to the British creditors.

President Francisco Robles, faced with the threat of the Peruvian blockade, moved the national capital to Guayaquil, and charged General José María Urbina with defending it.

[20] On May 1, a conservative triumvirate, integrated by Dr. Gabriel García Moreno, Pacífico Chiriboga and Jerónimo Carrión (Robles' vice president) formed the Provisional Government of Quito.

García Moreno fled to Peru, where he requested the support of President Castilla; the Peruvian leader supplied him with weapons and ammunition to subvert the Robles regime.

[19] When he received word of Franco's allegiance with Castilla, Robles disavowed their treaty, and moved the capital, this time to Riobamba, where he handed over leadership of the government to Jerónimo Carrión.

With the domestic situation at its most tumultuous, and the Peruvian blockade of the rest of the Ecuadorian coast nearing the end of its first year in place, Castilla sought to take advantage of the circumstances to impose a favorable border settlement.

[26] On September 20, Castilla wrote to Quito to declare his support for the Provisional Government; ten days later, he sailed from Callao, leading an invasion force.

[19] While stopped over in the port of Paita, in Peru, Castilla proposed to the Ecuadorians that they form a sole government with which they could negotiate an agreement to end the blockade and the territorial dispute.

[23] Castilla ordered his troops, 5,000 strong,[26] to disembark on Ecuadorian territory; the Peruvians set up camp at the hacienda of Mapasingue, near Guayaquil.

In an unsuccessful attempt to seek a powerful ally, García Moreno sent a series of secret[29] letters to the chargé d'affaires of France, Emile Trinité, on December 7, 15 and 21; in them, he proposed that Ecuador become a protectorate of the European country.