The Third Militarism () was the period between 1930 and 1939 in Peruvian history, in which Peru was ruled by a series of military governments.

In 1930, dictator of Peru, Augusto B. Leguia, was ousted by military forces led by Luis Miguel Sánchez Cerro in the 1930 Peruvian coup d'état, ending his regime known as the Oncenio. Sánchez Cerro ruled Peru as leader of a military junta for 6 months, which oversaw the liquidation of the Oncenio and the rise of the left-wing American Popular Revolutionary Alliance (APRA) in politics. By 1931, he was forced to resign due to opposition from several sectors of the nation. After a month of political instability with 3 temporary presidents, David Ocampo assumed the presidency for 8 months and reformed the electoral law until elections were called, which Sánchez Cerro won.

Sánchez Cerro's 2-year presidency (1931–1933) was marked by heavy repression of APRA, through the use of martial law and arresting many of the party's followers, known as Apristas. The Apristas fought back, conspiring with dissident military officers and starting uprisings, such as the 1932 Trujillo uprising. In the same year, Peruvian forces illegally marched into Colombia, beginning a border conflict known as the Colombia–Peru War which lasted a year. In 1933, Sánchez Cerro was assassinated, which led to General Oscar Benavides taking power.

Benavides' regime (1933–1939) was initially conciliatory and hoped to build a rapport between APRA and the government. However, discord between the two parties erupted soon after, and conflict began again. His term was meant to end in 1936, with a new president being elected in the 1936 Election. However, when Luis A. Eguiguren won with votes of the banned APRA, the results were declared invalid and Benavides' term was extended to 1939. For the remainder of his term, he focused on large-scale infrastructural and economic development of Peru, which helped to pacify the political scene against him. Following a failed coup d'état against him, new elections were held in 1939. Manuel Prado Ugarteche was declared the winner, restoring civilian rule in Peru.

Background Downfall of the Oncenio In 1919, president of Peru (1908–1912) Augusto B. Leguía, carried out a coup d'état, leading to the establishment of an 11-year period (known as the ) from 1919 to 1930 in which he ruled the country as a dictator.

In 1929, the United States stock market crashed, beginning a worldwide economic crisis known as the Great Depression. Built on economic support from the United States and foreign corporations, the Peruvian economy took a heavy toll and the country's banks went bankrupt. Export prices of copper, wool, and cotton fell as much as 70 percent. Mass unemployment was an issue, with mining industry, government bureaucracy, and the middle-class working as clerks most affected. This was a partly a result of all public works being discontinued. Leguía was ultimately blamed for the crisis. The army had also turned against Leguía after he ceded Arica to Perú and also because of their views that Leguía was favouring other branches of the military. Regional elites also opposed him for his centralisation policy. He had little supporters by the end of his regime.

Coup d'état of 1930

On 22 August 1930, Lieutenant Colonel Luis Miguel Sánchez Cerro, with the aid of civilian political leaders in Arequipa, led a coup d'état against the Leguía regime. Sánchez Cerro proclaimed himself: "Commander in Chief of the Southern Army" and: "Chief as Government", in which he guaranteed that all commercial and civil activities would function as normal in Arequipa for all residents of the city, which would be enforced by his rebel militia. On the same day, he appointed his secretaries who were:

(Military Affairs) José Luis Bustamante y Rivero (Political Affairs) Manuel A. Vinelli (Financial and Administrative Affairs) Major Rubén del Castillo (Postal Affairs and Transmissions); Major Julio Arboleda Viñas (Transportation and Communications) Gustavo de la Jara (Controller General).

The morning newspapers initially proclaimed the government's confidence in quelling the rebellion. The country's official newspaper stated that: "The country returns smoothly to normal as of on railway roadtracks". However, support for the rebellion began to unravel in Lima, the capital city. As rumors circulated that the entire south of the nation was in support of the movement, small groups of individuals and orators began marching down city streets and shouting verbal insults at the regime.

A manifesto was also written by Sánchez Cerro, known as the Arequipa Manifesto, which was distributed to the troops on August 22 which outlined his political intentions for Peru in the case of his victory.

Garrisons in the cities of Cuzco and Puno quickly rallied to Sánchez Cerro's side, and opposition quickly mounted against Leguía in Lima. He resigned and escaped on the cruiser Almirante Grau. For reasons which have been subject of historical debate, he arrived back to Peru at Callao, where he was arrested, detained and later exiled from Peru.

Military junta, 1930

Overview Sánchez Cerro's arrival in Lima was enthusiastically received by the popular masses; he gained their support and was elevated to the status of a national hero.

There was opposition to him from the upper-classes. Many intellectuals disliked him due to his lack of a political philosophy, while Aristocrats were still conscious of his partly-negro () skin colour, though it was a trait that enhanced his appeal to young members of the army. Sánchez Cerro was supportive of Indian rights in Peru, stating that he would "dignify and give homage to our Indian brothers." And that they would "constitute the heart of our national program, and not in theory alone.”

Liquidation of the Oncenio With the overthrow of Leguía, the new government allowed political opponents of his regime, who had been exiled, to return to Peru. One such political opponent of Leguía was Victor Raúl Haya de la Torre, who had founded the American Popular Revolutionary Alliance (APRA) in 1924; a leftist anti-Leguia party founded by Mexican students who had been exiled from Peru. With the collapse of the Oncenio, APRA quickly rose to importance in the political scene following the aftermath of the 1930 coup d'état.

Civilians looted and burned the houses of Leguia's supporters (referred to as ). Stoked by press censorship during the Oncenio, a witch-hunt began against associates of the Leguía regime. Newspapers began a series of exposés against Leguiístas, with the most popular ones including stories of their corruption and wealth. The anti-leguia newspaper directed by Fransico A. Loayza, reached 70000 to 80000 copies in distribution.

Actions of the government Sánchez Cerro used Leguía's unpopularity to consolidate his political power. He imprisoned Leguía and his Leguiístas through the Tribunal of National Sanction, and made reference to the fall of the Leguía regime in nearly all his speeches.

Sánchez Cerro abolished the , a forced public work programme introduced by Leguia, which garnered him popularity among the native Indian community, as the programme had exploited them for labour. He criminalised enforcement of the road tax, a law that though repealed in 1856, continued to be enforced by large landowners; which also mainly targeted the Indian population which used the road for trade of goods. He also ordered gates along roads intentionally made to obstruct traffic flow to be demolished by local officials. Another measure that earned Sánchez Cerro popular favor was the legalization of civil marriage and divorce, which passed with unanimous support despite protests from Catholic ranks and various splintered reactionary groups. These measures were mainly taken to ensure that the urban poor would support him in the upcoming elections.

Relations with APRA Upon his presidential inauguration, several groups consisting of aristocratic elements were formed which aimed to remove Sánchez Cerro from power and install one of their own in the presidency. He was also challenged by Gustavo A. Jiménez, (later his minister of government) a pro-APRA political figure who shared the same motives as the party—in that—in order for Peru to solve its problems, the country needed to wage warfare against its upper classes.

After establishing a brief alliance with APRA against the Leguiístas, he was forced to repress it due to the influence of foreign firms which dominated Peru's export economy of 1930. In October 1930, workers in the mining camps were unionised by the Peruvian Communist Party (PCP) and called a strike. In response, the PCP was heavily repressed as a result, and APRA emerged on the as the only viable alternative on the left-leaning political scene . Sánchez Cerro and his APRA-leaning minister of government, Gustavo Jiménez, were slow to respond, and as a result, faced a campaign of strong pressure from foreign mining and oil firms together with British and American embassies. Their aim was to have APRA repressed and Jiménez dismissed for his pro-worker sympathies. A clash broke out between police forces and the strikers at Malpaso, leaving a number of workers dead and triggering riots, leading Cerro Corporation to close down its company, and demand terms to the government. Still in the aftermath of the great depression, he had no choice but to accept these terms. Following the incident, he would continuously repress APRA for the rest of his term.

Relations with labour Nevertheless, Sanchez Cerro's junta still attempted to appeal to labour in general. Following the Arequipa revolution, a number of progressives and radicals were given positions in the newly revamped Sección de Trabajo, with Erasmo Roca appointed as its direction of development. Included in its ranks was also Angela Ramos, a member of the communist party. One of the first measures it took was to organise a labour exchange, which would alleviate the growing number of those unemployed in Lima. In September 1930, it also approved the creation of regional labor inspectorates. This was born out of Roca's desire to expand the Sección de Trabajo out of Lima.

End of the military junta Sánchez Cerro's efforts to arrange a presidential election brought opposition to his government and hostility from the press. Hostility also came from senior officers in the armed forces, who resented having to obey a lower-ranked officer. Some junior officers who had not been promoted after their participation in the 1930 coup'd'tat also felt indignant as to how they had been treated. The result was a series of military revolts which sprung up throughout the country in February, with participation from some parts of the former Leguía regime. Sánchez Cerro could not resolve the situation, and resigned on March 1.

Political crisis and 'Ocampo's junta Following Sanchez Cerro's resignation, archbishop Mariano Holguín assumed the presidency for a few hours before it was handed over to Leoncio Elías. Elías formed a Military Junta, however its unpopularity led him to hand over power to David Samanez Ocampo after a meeting on 4 March 1931. This transfer of power never happened as Gustavo Jiménez overthrew Elías on 5 March, but Ocampo's popularity forced him to hand power back to him on 10 March.

Ocampo's junta During Ocampo's brief tenure, he reformed the electoral law in March 1931, by abolishing property requirements for voting and introducing the secret ballot, these changes expanded the electorate by 59%. He also transferred power to supervise elections from provincial authorities to departmental authorities. These changes reduced the ability of wealthy landowners (Colloquially called ) to dominate elections and opened more electoral prospects for parties whose support was based on the popular masses. They may have been made with the intention of improving APRA's chances of an electoral victory.