During this era, what became known as the First Militarism (Spanish: Primer Militarismo), a period where several military figures held control of the country, started in 1827 with José de La Mar's presidency, ending in 1844.

After the Independence of Chile, General José de San Martín, on August 20, 1820, at the head of the Liberating Expedition of Peru, set sail from Valparaíso and landed in the Bay of Paracas in September of that year.

Long live independence!San Martín had assumed the military and political command of the so-called free departments of Peru under the title of Protector, as stated in the decree of August 3, 1821.

However, he was aware of the numerical inferiority of his forces, compared to that of the viceregals who dominated the interior of the country from Jauja to Upper Peru, and numbered a total of 23,000 soldiers, mostly Andean and mestizo recruits.

Indeed, during the Guayaquil meeting, Bolívar offered San Martín military aid to Peru, which materialized in July 1822, with the sending of troops under the command of Juan Paz del Castillo, but these were still insufficient.

However, the Junta could not obtain the support of the government of Buenos Aires, overwhelmed by internal difficulties, and did not grant the army that garrisoned Lima the necessary means to timely initiate an offensive into the central mountains.

Then he headed to Arica, where he remained without disembarking for three weeks, giving time for Viceroy La Serna, informed by his espionage service of the patriot presence, to order his lieutenants José de Canterac and Gerónimo Valdés to go with their forces to the threatened area.

The patriotic officers in command of the troops that garrisoned Lima, fearing a Spanish offensive, signed a request before Congress, dated February 23, 1823 in Miraflores, invoking the designation of a single Supreme Chief "to order and be quickly obeyed”, replacing the collegiate body that made up the Junta.

It also created a military power that he entrusted to the Venezuelan general Antonio José de Sucre (who had arrived in Peru in May of that year, at the head of the first Colombian troops), and accredited a delegation to request the personal collaboration of Simón Bolívar in the war on June 19, 1823.

But before the civil war broke out, Riva-Agüero was captured by his own officers led by Colonel Antonio Gutiérrez de la Fuente, who, disobeying the order to shoot him, banished him to Guayaquil on November 25, 1823.

The royalists, aware of Bolívar's illness, took advantage of the situation and managed to get the patriotic troops (from the River Plate and Chile) who were garrisoning the Real Felipe Fortress in Callao, to mutiny, demanding accrued payments and other mistreatment.

While Bolívar prepared everything related to the final campaign of independence from his headquarters in Trujillo, Sucre toured the terrain in the mountains, and with the protection of the Montoneros he drew up sketches and plans of the territory that would inevitably be the scene of the war.

Canterac found out late about the patriot advance because he did not have a good spy service and decided to go out to meet the adversary, leaving Jauja on August 10 with 7,000 infantry men and 1,300 cavalry, heading towards Cerro de Pasco.

Canterac, after the battle of Junín, pursued by the Montoneros of Colonels Marcelino Carreño, Otero, Terreros, by Commander Peñaloza, by Major Astete, headed south along the banks of the Mantaro River.

Sucre then opened a campaign in said territory, counting on the collaboration of General Juan Antonio Álvarez de Arenales who, in his capacity as governor of the Argentine province of Salta, prepared to attack this region.

Another Spanish soldier who refused to abide by the terms of the capitulation was José Ramón Rodil who, in command of the Real Felipe Fortress in Callao (which had returned to royalist power in February 1824), remained stubbornly loyal to the king of Spain.

This provoked the anger of Bolívar, who in a letter addressed to Antonio Gutiérrez de la Fuente (then prefect of Arequipa) complained about the "damned deputies" that he had sent to his jurisdiction, asking him to do something to change them.

On September 1, 1826, the same day that the third anniversary of his arrival in Peru was celebrated, Bolívar announced his definitive retirement, but at the insistent request of some ladies of Lima's society, he promised to stay, but on the 3rd of that month, he embarked on the brig Congreso, heading to Colombia, where he calmed things down, although for a short time.

The General Constituent Congress of Peru [es] (the second in Peruvian republican history) was established on June 4, 1827, with 83 deputies elected by provinces, including Maynas (territory that Bolívar already claimed as part of Colombia at that time).

The Minister in charge of Finance, José de Morales y Ugalde [es], presented to Congress an extensive report of everything done within his branch in the past government and a list of public receipts and expenses in 1827.

The Constituent Congress gave the liberal Constitution of 1828, the second that the Republic of Peru had, whose promulgation and public oath was scheduled for April 5, 1828, which had to be postponed until the 18th of that month, due to having On March 30, a tremendous earthquake occurred in Lima that left the city almost in ruins.

After a triumphant walk through Bolivian territory, with hardly any resistance, he signed the Treaty of Piquiza with the government of Urdininea on July 6, 1828, in which it was agreed, among other things, the withdrawal of the Colombian troops from Bolivia and the resignation of the presidency by Sucre.

After the treaty was signed, an error on Sucre's part led to controversy: he had ordered that a monument be erected at Tarqui which stated that an army of 8,000 Peruvians who "invaded the land of their liberators" was defeated at the site.

La Mar refused to do so, and he was immediately transferred to the port of Paita, where at dawn on the 9th he was embarked along with Colonel Pedro Pablo Bermúdez and six black slaves, on a miserable schooner called "Las Mercedes", bound for Costa Rica, where he would die on October 11, 1830.

On November 8, 1831, the same plenipotentiaries, with the mediation of Chile, signed the Treaty of Peace and Friendship in Arequipa, which ratified the previous agreements, in addition to the prohibition of seditious activities for political refugees from both countries, and the maintenance of borders until the appointment of boundary commissions.

Fearing a coup d'état, Orbegoso decided to leave Lima and took refuge in the Real Felipe Fortress of Callao on January 3, 1834, where he installed the headquarters of his government and began to relieve the Gamarristas of the high command of the Army.

At the national level, Bermúdez's authority was respected by some garrisons: in Cuzco, with the prefect Juan Ángel Bujanda [es] at the head; in Puno, with Miguel de San Román; in Ayacucho with Frías.

The consul of Chile, Don Ventura Lavalle, wrote to his government, referring to the leader in the following way: "Salaverry is a young man who is going to give his countrymen a lot of work, because a screwed-up head, excessive ambition and a haughty character and bloodthirsty, brings together talent and courage not common in the country."

While these events were occurring in Peru, in Bolivia, President Andrés de Santa Cruz and General Agustín Gamarra were outlining plans to reunite both countries into a single Federal Republic.

Following these plans and without waiting for a formal agreement with Santa Cruz, on May 20, 1835, Gamarra crossed the Desaguadero border and entered Peru, occupying the cities of Puno and Cuzco, areas where he had numerous supporters.