In the National Assembly "National Assembly of Peru (1919)") the Constitution of 1920 was approved, which replaced the Constitution of 1860.

The new Constitution established a presidential term of five years (although at the moment it did not contemplate immediate re-election); the comprehensive renewal of parliament parallel to the presidential renewal; the regional congresses in the north, center and south; the semi-parliamentary regime; the responsibility of the cabinet before each of the chambers; the recognition of indigenous communities; the impossibility of suspending individual guarantees, etc.[6]​.

One of the most important characteristics of this Constitution was its protection of indigenous peoples and communities.[7] Thus, article 58 of said Constitution establishes that:

In turn, article 41 stated that the assets of indigenous communities are imprescriptible, thus protecting communally owned lands.[8]​.

But many of the progressive constitutional innovations were not implemented and remained only on paper.

Although in theory Leguía wanted to adhere to the Constitution and run a government with respect for democratic principles, in practice his government restricted public freedoms. In September 1919, the printing presses of the newspapers El Comercio "El Comercio (Perú)") and La Prensa "La Prensa (Perú)") were attacked by mobs with obvious government leadership.[4]La Prensa, where the opposition had taken refuge, was confiscated. In this way, freedom of expression was practically subjugated.[9] The opposition in Congress was also swept away, which was submitted to the Executive. The deputies Jorge and Manuel Prado Ugarteche, the first for the province of Dos de Mayo, and the second for that of Huamachuco, were arrested and exiled.[10]​.

On the other hand, it ended with the Municipalities elected by popular vote to replace them with personnel appointed by the government (the so-called Boards of Notables).[11]​.

Opponents of the government were persecuted, imprisoned, deported and even shot. Prominent among the exiles is the then young student leader Víctor Raúl Haya de la Torre, who led the famous protest in Lima against the consecration of the Sacred Heart of Jesus to the government on May 23, 1923, in which a worker and a student died.[12] In exile, Haya founded APRA, a party with continental projection initially with anti-imperialist and anti-oligarchic ideology. Other opponents of the government, such as the young journalists José Carlos Mariátegui and César Falcón, were sent to Europe on scholarships. Mariátegui, upon returning to Peru, founded the Peruvian Socialist Party.[13]​.

Other exiles were Colonel Óscar R. Benavides (former president of Peru), Arturo Osores, [14] Luis Fernán Cisneros and Víctor Andrés Belaúnde. The island of Taquile, in Lake Titicaca, fulfilled the same purpose.[16]​.

The modernization of the country had already been tested by previous governments, but under the Oncenio of Leguía it received its definitive impetus. The main bases of this modernizing leap were the following:

Without a doubt the most resonant event of this period was the apotheosis celebration of the Centennial of Independence (July 28, 1921). 29 foreign delegations arrived from countries in America, Europe and Asia, with notable absences from Venezuela (whose government mistakenly believed that the Liberator Bolívar had been excluded from the tributes) and Chile (which was not invited because it had a territorial conflict with Peru). Authorities and people in general spared no effort to magnificently celebrate the Centennial, despite the fire that devastated the Government Palace, among other difficulties. This fire occurred on July 3, 1921, destroying the ground floor of the Palace, although, by order of Leguía, it was rebuilt in the following weeks, leaving the premises ready to receive the delegations and special guests to the Centennial party.[17]​.

Each friendly nation made a gift to Peru, among the main ones, the National Stadium (United Kingdom); the Museum of Italian Art (Italy); the clock tower of the University Park (Germany); the water fountain in the Exhibition Park (China); the monument to Labor (Belgium); the Moorish Arch, which was built at the beginning of Avenida Arequipa (then called Avenida Leguía), a gift from the Spanish colony; the monument to Manco Cápac, in Plaza Leguía, a gift from the Japanese colony; and others.[18]​[19]​.

There were sumptuous parties in the Government Palace, in the clubs, gala horse races, popular festivals, the great military parade, school parades, float parades, and a series of inaugurations.[20]​.

One of the most emotional acts was, without a doubt, the inauguration of the monument "Monumento a San Martín (Lima)") to Generalissimo José de San Martín, in the square that has since carried his name "Plaza San Martín (Lima)").[18]​.

In December 1924, lavish celebrations were held again in Lima and Ayacucho, this time on the occasion of the first centenary of the battle of Ayacucho, the same one that had sealed the independence of Peru and continental America. On that occasion, the Gran Hotel Bolívar (in front of Plaza San Martín) and the monuments to Admiral Du Petit Thouars and Marshal Sucre were inaugurated, the latter in a square next to the Parque de la Reserva.[19]​.

Leguía faced the thorny issue of La Brea and Pariñas. This was a lawsuit that consisted of the American company International Petroleum Company (IPC, a subsidiary of Standard Oil of New Jersey) exploiting the oil fields of La Brea and Pariñas (northern Peru) without contributing to the treasury the real amount of taxes to which it was obliged according to Peruvian law, taking advantage of an old error in the measurement of belongings. Congress in 1918 had agreed that the matter be submitted to international arbitration.[21] But Leguía, under pressure from the US government, preferred to reach a transactional agreement. This was signed on March 2, 1922, between the Peruvian Foreign Minister Alberto Salomón and the English representative Mr. A. C. Grant Duff. This Salomón-Grant Duff Transactional Agreement was presented to the Arbitration Court, which met in Paris and was made up of the president of the Swiss Federal Court and the representatives of the Peruvian and English governments. On April 24 of that year, 1922, without further discussion, they approved the Transactional Agreement to which they granted the status of Award, the conditions of which were binding on the high contracting parties as a solution to the controversy that arose.[22]​[23]​.

The agreements of the so-called Paris Award were the following:[24]​.

This arbitration award was, clearly, adverse to the interests of Peru, since it established a tax exception regime for the owners and exploiters of La Brea and Pariñas. The Treasury thus stopped receiving substantial amounts of money as taxes. The Leguía government thus set a precedent of submission to American interests that would give rise to nationalist protests over several decades.[25]​.

Another controversial agreement was the one signed with the Peruvian Corporation. Since 1890, this English company had been in charge of operating the national railways, which had to be for a specific period, as stipulated in the Grace Contract. In 1907, this period was extended until 1973. However, in 1928, the Leguía government signed a new exchange contract with Peruvian, by which it transferred the national railways in perpetuity in exchange for some compensation. In the 1970s, under the Revolutionary Government of the Armed Forces, this situation came to an end with the nationalization of the railways and their exploitation through the state company Enafer Perú.[26]​.

As the end of his term approached in 1924, Leguía had the article of the Constitution that prohibited immediate presidential re-election reformed, with the support of a submissive Congress. Even Germán Leguía y Martínez, his cousin and Minister of Government, opposed said re-election plan, for which he suffered imprisonment and exile.[27]​ Swept away all opposition, Leguía was re-elected in elections that did not have any guarantee and was sworn in for a new five-year presidential term (1924-1929).[28]​.

In 1929, as the end of his second consecutive government approached, Leguía proposed to reform the Constitution again, to allow his indefinite re-election. Congress made the amendment and Leguía was re-elected in other fraudulent elections, for a third consecutive period of five years, but which would only last until 1930.[29]​.

The opposition against the leguiista regime was increasing. Rebellions broke out in the provinces: in Cuzco, Puno, Loreto, Apurímac, Huacho, Chicama, and especially in Cajamarca.

Although Leguía founded the Patronato de la Raza Indígena and showed his interest in legalizing the communities,[33]​ during his government there were many indigenous rebellions, which were severely suppressed. One of the reasons for the discontent was the Road Conscription Law, which forced the population to work as laborers in road works.[34] Another reason was the abuse of gamonalismo, a system of exploitation of the peasants of the haciendas, characterized by its productivity and profitability, the waste of labor force and the cultural exclusion of its agricultural laborers. The gamonales held considerable local power and were the firmest propagators of the thesis of the racial inferiority of the indigenous people, calling it vices that they themselves tried to maintain, such as ignorance and the consumption of alcohol and coca. The indigenous communities continued, however, to subsist despite the fact that the gamonales made every effort to take away their lands and reduce the Indian to the status of serf.[35]​.

In 1921 there were massacres of indigenous people in Layo and Tocroyoc") (Cuzco). Between 1922 and 1927 there were a series of uprisings in Ayacucho, La Mar, Tayacaja, Huancané, Azángaro and Quispicanchis").[36]

A consequence of this discontent was the banditry that proliferated in the provinces. There was no province that did not have its famous bandit. Many of them even confronted each other, when they were not fleeing from law enforcement. A bandit was, properly speaking, a highway robber, but he could also have a political ideology and be a kind of Montonero who supported a leader or a political tendency. Famous bandits were Luis Pardo, who acted in the Huaylas alley; and Eleodoro Benel"), which had its radius of action in Cajamarca. The actions of the bandits have generally been marginalized by historians, with the literati having been in charge of preserving their memory, as can be seen in the works of Enrique López Albújar and Ciro Alegría.[37]​.

During the Oncenio, the first modern political parties of Peru emerged, which replaced the old or traditional ones that were already extinct or in decline (such as the Civil "Civil Party (Peru)"), the Democratic "Democratic Party (Peru)"), the Constitutional "Constitutional Party (Peru)") and the Liberal "Liberal Party (Peru)"). The main ones were:

Agricultural policy

Notable support was given to the development of agriculture and livestock.[65]​.

Mining policy

Various measures were taken to improve mining activity in the country.[66]​.

Government and Police

Special attention was given to the development of communications, the maintenance of public order and the improvement of police services.[68]​.

Labor policy

Following the trend of the advancement of the rights of workers and employees worldwide, Leguía was concerned with promoting laws in this regard.

National defense

In this field, war material was acquired, administration services were improved and the armed force was modernized in line with the advances in military technology worldwide.[71]​.

International aspect

Leguía, continuing his policy of defining international borders initiated in his first government (1908-1912), promoted the definitive border treaties with Colombia and Chile. In this regard, there is a nationalist current in Peru that has denigrated this policy, describing its border arrangements as supposedly "surrender." Although he may have made some mistakes, Leguía at least had the decision to definitively resolve old border conflicts that his predecessors had been prolonging in an irresponsible and dangerous manner.

Leguía began talks with Colombia to definitively resolve the border issue, which was tending to become a centenary, since it dated back to the time of independence. Colombia aspired to legitimize its border from the Caquetá River to the Putumayo River (territorial strip that Peru actually occupied, thanks to the actions of the Peruvian rubber tappers), as well as obtain access to the Amazon River.[83]​.

Previous Peruvian governments had refused to give in to Colombian claims, but Leguía, in his obsession to resolve the dispute once and for all, promoted the Salomón-Lozano Treaty, which was signed by the Peruvian chancellor Alberto Salomón and the Colombian minister Fabio Lozano Torrijos, in Lima, on March 24, 1922. This meant ceding to Colombia an extensive portion of territory between the Caquetá and Putumayo rivers (area in dispute) and the so-called Amazonian Trapeze, where the Peruvian population of Leticia "Leticia (Colombia)") was located, along the Amazon River. In this way, Colombia gained access to this river, which until then was only shared by Peru and Brazil. In compensation, Peru received the so-called San Miguel-Sucumbios Triangle,[84][85]​ which in practice it never occupied and which in 1942 it would cede to Ecuador.[86]​.

The treaty was approved by the Congress submissive to Leguía in 1927 and was put into execution on August 17, 1930, a few days before the fall of Leguía.[87]​ When the treaty was made public, it caused great resistance among the Peruvians who lived in the affected areas, thus arising a state of conflict between both nations that would worsen in 1932.[88]​.

It was said that Leguía signed this treaty with Colombia under pressure from the United States, which wanted to somehow compensate Colombia for Panama's independence. But geopolitical calculations must also have taken precedence in Leguía: with the treaty, Colombia was gained as an ally, which until then had been close to Ecuador in its claim to Peruvian Amazon territories. In fact, upon learning of the signing of the treaty, Ecuador broke relations with Colombia. And a Colombian-Ecuadorian alliance against Peru would have had disastrous consequences for the latter, without a doubt.[89]​.

Peruvian historians such as Jorge Basadre and Gustavo Pons Muzzo agree that the Salomón-Lozano Treaty was an error in Leguía's diplomacy, considering that Colombia came out with a greater advantage in the territorial cession and that Peru renounced a policy of defense of its territory that it had maintained until then unchanged.[90]​[88]​ This interpretation is the one that has been perpetuated in Peruvian teaching and the one that has given rise to the black legend of Leguía. On the other hand, in Colombia it is considered that it was a transactional agreement, that is, that both parties renounced their maximum claims, made mutual concessions and reached a balanced agreement.

Leguía also proposed to definitively resolve the problem with Chile regarding the question of Tacna and Arica. As the years passed, the plebiscite initially agreed upon in the Treaty of Ancón of 1883 to decide the fate of the Peruvian provinces of Tacna and Arica, held captive in Chile since the Pacific War of 1879-1883, became unattainable.[91]​.

When the dispute was submitted to the arbitration of the President of the United States Calvin Coolidge, he gave his ruling (award) on March 4, 1925, resolving to hold the plebiscite. This award was not well received by Peruvian public opinion, too aware of Chile's behavior towards these provinces, which it had subjected to a heartless policy of "Chileanization" for many years. Indeed, the American commissioners who came to supervise the plebiscite, Generals John J. Pershing and William Lassiter, verified that it was impracticable due to the lack of minimum conditions for a fair and objective popular consultation.[92]​[93]​.

The plebiscite did not take place and both parties returned to direct negotiations, which culminated in the treaty signed on June 3, 1929, in Lima, between the Peruvian chancellor Pedro José Rada y Gamio and the Chilean representative Emiliano Figueroa Larraín (which is why it is also known as the Rada y Gamio-Figueroa Larraín Treaty). Both parties definitively renounced the holding of the plebiscite with the following arrangement: Tacna would return to the heart of the Peruvian homeland, but Chile would remain with Arica. In addition, other concessions were granted to Peru in Arica, such as a dock and its customs infrastructure, possession of the House of Response, possession of the Tacna-Arica railway station and the route of its line, the water sources of the Uchusuma and Maure, among other easements.[94][95]​.

On August 28, 1929, Tacna was reincorporated into Peru.

The world crisis of 1929 had very serious effects on the national economy of Peru. The working sectors, directly affected by the rise in the cost of living and the scarcity of subsistence, were the first to raise their protest. The army also showed its discontent. The evident administrative corruption, from which close associates or friends of the president benefited throughout the regime, as well as the signing of treaties with Colombia and Chile with territorial transfer, further accentuated opposition to the government. Subversive actions and assassination attempts on the president were rumored.

On August 22, 1930, Commander Luis Miguel Sánchez Cerro, in command of the Arequipa garrison, spoke out against the government. The revolutionary movement spread quickly through the south of the country. Also in Lima the atmosphere was favorable for the revolution. To dominate the situation, Leguía attempted to form a military cabinet, but in the early hours of the morning on August 25, the Lima garrison requested his resignation.[99]​.

Leguía accepted and resigned command, which remained in the hands of a Military Government Junta chaired by General Manuel María Ponce Brousset.[100]​ Two days later he would hand over power to Sánchez Cerro, who arrived in the capital by plane.[101]​.

In the National Assembly "National Assembly of Peru (1919)") the Constitution of 1920 was approved, which replaced the Constitution of 1860.

The new Constitution established a presidential term of five years (although at the moment it did not contemplate immediate re-election); the comprehensive renewal of parliament parallel to the presidential renewal; the regional congresses in the north, center and south; the semi-parliamentary regime; the responsibility of the cabinet before each of the chambers; the recognition of indigenous communities; the impossibility of suspending individual guarantees, etc.[6]​.

One of the most important characteristics of this Constitution was its protection of indigenous peoples and communities.[7] Thus, article 58 of said Constitution establishes that:

In turn, article 41 stated that the assets of indigenous communities are imprescriptible, thus protecting communally owned lands.[8]​.

But many of the progressive constitutional innovations were not implemented and remained only on paper.

Although in theory Leguía wanted to adhere to the Constitution and run a government with respect for democratic principles, in practice his government restricted public freedoms. In September 1919, the printing presses of the newspapers El Comercio "El Comercio (Perú)") and La Prensa "La Prensa (Perú)") were attacked by mobs with obvious government leadership.[4]La Prensa, where the opposition had taken refuge, was confiscated. In this way, freedom of expression was practically subjugated.[9] The opposition in Congress was also swept away, which was submitted to the Executive. The deputies Jorge and Manuel Prado Ugarteche, the first for the province of Dos de Mayo, and the second for that of Huamachuco, were arrested and exiled.[10]​.

On the other hand, it ended with the Municipalities elected by popular vote to replace them with personnel appointed by the government (the so-called Boards of Notables).[11]​.

Opponents of the government were persecuted, imprisoned, deported and even shot. Prominent among the exiles is the then young student leader Víctor Raúl Haya de la Torre, who led the famous protest in Lima against the consecration of the Sacred Heart of Jesus to the government on May 23, 1923, in which a worker and a student died.[12] In exile, Haya founded APRA, a party with continental projection initially with anti-imperialist and anti-oligarchic ideology. Other opponents of the government, such as the young journalists José Carlos Mariátegui and César Falcón, were sent to Europe on scholarships. Mariátegui, upon returning to Peru, founded the Peruvian Socialist Party.[13]​.

Other exiles were Colonel Óscar R. Benavides (former president of Peru), Arturo Osores, [14] Luis Fernán Cisneros and Víctor Andrés Belaúnde. The island of Taquile, in Lake Titicaca, fulfilled the same purpose.[16]​.

The modernization of the country had already been tested by previous governments, but under the Oncenio of Leguía it received its definitive impetus. The main bases of this modernizing leap were the following:

Without a doubt the most resonant event of this period was the apotheosis celebration of the Centennial of Independence (July 28, 1921). 29 foreign delegations arrived from countries in America, Europe and Asia, with notable absences from Venezuela (whose government mistakenly believed that the Liberator Bolívar had been excluded from the tributes) and Chile (which was not invited because it had a territorial conflict with Peru). Authorities and people in general spared no effort to magnificently celebrate the Centennial, despite the fire that devastated the Government Palace, among other difficulties. This fire occurred on July 3, 1921, destroying the ground floor of the Palace, although, by order of Leguía, it was rebuilt in the following weeks, leaving the premises ready to receive the delegations and special guests to the Centennial party.[17]​.

Each friendly nation made a gift to Peru, among the main ones, the National Stadium (United Kingdom); the Museum of Italian Art (Italy); the clock tower of the University Park (Germany); the water fountain in the Exhibition Park (China); the monument to Labor (Belgium); the Moorish Arch, which was built at the beginning of Avenida Arequipa (then called Avenida Leguía), a gift from the Spanish colony; the monument to Manco Cápac, in Plaza Leguía, a gift from the Japanese colony; and others.[18]​[19]​.

There were sumptuous parties in the Government Palace, in the clubs, gala horse races, popular festivals, the great military parade, school parades, float parades, and a series of inaugurations.[20]​.

One of the most emotional acts was, without a doubt, the inauguration of the monument "Monumento a San Martín (Lima)") to Generalissimo José de San Martín, in the square that has since carried his name "Plaza San Martín (Lima)").[18]​.

In December 1924, lavish celebrations were held again in Lima and Ayacucho, this time on the occasion of the first centenary of the battle of Ayacucho, the same one that had sealed the independence of Peru and continental America. On that occasion, the Gran Hotel Bolívar (in front of Plaza San Martín) and the monuments to Admiral Du Petit Thouars and Marshal Sucre were inaugurated, the latter in a square next to the Parque de la Reserva.[19]​.

Leguía faced the thorny issue of La Brea and Pariñas. This was a lawsuit that consisted of the American company International Petroleum Company (IPC, a subsidiary of Standard Oil of New Jersey) exploiting the oil fields of La Brea and Pariñas (northern Peru) without contributing to the treasury the real amount of taxes to which it was obliged according to Peruvian law, taking advantage of an old error in the measurement of belongings. Congress in 1918 had agreed that the matter be submitted to international arbitration.[21] But Leguía, under pressure from the US government, preferred to reach a transactional agreement. This was signed on March 2, 1922, between the Peruvian Foreign Minister Alberto Salomón and the English representative Mr. A. C. Grant Duff. This Salomón-Grant Duff Transactional Agreement was presented to the Arbitration Court, which met in Paris and was made up of the president of the Swiss Federal Court and the representatives of the Peruvian and English governments. On April 24 of that year, 1922, without further discussion, they approved the Transactional Agreement to which they granted the status of Award, the conditions of which were binding on the high contracting parties as a solution to the controversy that arose.[22]​[23]​.

The agreements of the so-called Paris Award were the following:[24]​.

This arbitration award was, clearly, adverse to the interests of Peru, since it established a tax exception regime for the owners and exploiters of La Brea and Pariñas. The Treasury thus stopped receiving substantial amounts of money as taxes. The Leguía government thus set a precedent of submission to American interests that would give rise to nationalist protests over several decades.[25]​.

Another controversial agreement was the one signed with the Peruvian Corporation. Since 1890, this English company had been in charge of operating the national railways, which had to be for a specific period, as stipulated in the Grace Contract. In 1907, this period was extended until 1973. However, in 1928, the Leguía government signed a new exchange contract with Peruvian, by which it transferred the national railways in perpetuity in exchange for some compensation. In the 1970s, under the Revolutionary Government of the Armed Forces, this situation came to an end with the nationalization of the railways and their exploitation through the state company Enafer Perú.[26]​.

As the end of his term approached in 1924, Leguía had the article of the Constitution that prohibited immediate presidential re-election reformed, with the support of a submissive Congress. Even Germán Leguía y Martínez, his cousin and Minister of Government, opposed said re-election plan, for which he suffered imprisonment and exile.[27]​ Swept away all opposition, Leguía was re-elected in elections that did not have any guarantee and was sworn in for a new five-year presidential term (1924-1929).[28]​.

In 1929, as the end of his second consecutive government approached, Leguía proposed to reform the Constitution again, to allow his indefinite re-election. Congress made the amendment and Leguía was re-elected in other fraudulent elections, for a third consecutive period of five years, but which would only last until 1930.[29]​.

The opposition against the leguiista regime was increasing. Rebellions broke out in the provinces: in Cuzco, Puno, Loreto, Apurímac, Huacho, Chicama, and especially in Cajamarca.

Although Leguía founded the Patronato de la Raza Indígena and showed his interest in legalizing the communities,[33]​ during his government there were many indigenous rebellions, which were severely suppressed. One of the reasons for the discontent was the Road Conscription Law, which forced the population to work as laborers in road works.[34] Another reason was the abuse of gamonalismo, a system of exploitation of the peasants of the haciendas, characterized by its productivity and profitability, the waste of labor force and the cultural exclusion of its agricultural laborers. The gamonales held considerable local power and were the firmest propagators of the thesis of the racial inferiority of the indigenous people, calling it vices that they themselves tried to maintain, such as ignorance and the consumption of alcohol and coca. The indigenous communities continued, however, to subsist despite the fact that the gamonales made every effort to take away their lands and reduce the Indian to the status of serf.[35]​.

In 1921 there were massacres of indigenous people in Layo and Tocroyoc") (Cuzco). Between 1922 and 1927 there were a series of uprisings in Ayacucho, La Mar, Tayacaja, Huancané, Azángaro and Quispicanchis").[36]

A consequence of this discontent was the banditry that proliferated in the provinces. There was no province that did not have its famous bandit. Many of them even confronted each other, when they were not fleeing from law enforcement. A bandit was, properly speaking, a highway robber, but he could also have a political ideology and be a kind of Montonero who supported a leader or a political tendency. Famous bandits were Luis Pardo, who acted in the Huaylas alley; and Eleodoro Benel"), which had its radius of action in Cajamarca. The actions of the bandits have generally been marginalized by historians, with the literati having been in charge of preserving their memory, as can be seen in the works of Enrique López Albújar and Ciro Alegría.[37]​.

During the Oncenio, the first modern political parties of Peru emerged, which replaced the old or traditional ones that were already extinct or in decline (such as the Civil "Civil Party (Peru)"), the Democratic "Democratic Party (Peru)"), the Constitutional "Constitutional Party (Peru)") and the Liberal "Liberal Party (Peru)"). The main ones were:

Agricultural policy

Notable support was given to the development of agriculture and livestock.[65]​.

Mining policy

Various measures were taken to improve mining activity in the country.[66]​.

Government and Police

Special attention was given to the development of communications, the maintenance of public order and the improvement of police services.[68]​.

Labor policy

Following the trend of the advancement of the rights of workers and employees worldwide, Leguía was concerned with promoting laws in this regard.

National defense

In this field, war material was acquired, administration services were improved and the armed force was modernized in line with the advances in military technology worldwide.[71]​.

International aspect

Leguía, continuing his policy of defining international borders initiated in his first government (1908-1912), promoted the definitive border treaties with Colombia and Chile. In this regard, there is a nationalist current in Peru that has denigrated this policy, describing its border arrangements as supposedly "surrender." Although he may have made some mistakes, Leguía at least had the decision to definitively resolve old border conflicts that his predecessors had been prolonging in an irresponsible and dangerous manner.

Leguía began talks with Colombia to definitively resolve the border issue, which was tending to become a centenary, since it dated back to the time of independence. Colombia aspired to legitimize its border from the Caquetá River to the Putumayo River (territorial strip that Peru actually occupied, thanks to the actions of the Peruvian rubber tappers), as well as obtain access to the Amazon River.[83]​.

Previous Peruvian governments had refused to give in to Colombian claims, but Leguía, in his obsession to resolve the dispute once and for all, promoted the Salomón-Lozano Treaty, which was signed by the Peruvian chancellor Alberto Salomón and the Colombian minister Fabio Lozano Torrijos, in Lima, on March 24, 1922. This meant ceding to Colombia an extensive portion of territory between the Caquetá and Putumayo rivers (area in dispute) and the so-called Amazonian Trapeze, where the Peruvian population of Leticia "Leticia (Colombia)") was located, along the Amazon River. In this way, Colombia gained access to this river, which until then was only shared by Peru and Brazil. In compensation, Peru received the so-called San Miguel-Sucumbios Triangle,[84][85]​ which in practice it never occupied and which in 1942 it would cede to Ecuador.[86]​.

The treaty was approved by the Congress submissive to Leguía in 1927 and was put into execution on August 17, 1930, a few days before the fall of Leguía.[87]​ When the treaty was made public, it caused great resistance among the Peruvians who lived in the affected areas, thus arising a state of conflict between both nations that would worsen in 1932.[88]​.

It was said that Leguía signed this treaty with Colombia under pressure from the United States, which wanted to somehow compensate Colombia for Panama's independence. But geopolitical calculations must also have taken precedence in Leguía: with the treaty, Colombia was gained as an ally, which until then had been close to Ecuador in its claim to Peruvian Amazon territories. In fact, upon learning of the signing of the treaty, Ecuador broke relations with Colombia. And a Colombian-Ecuadorian alliance against Peru would have had disastrous consequences for the latter, without a doubt.[89]​.

Peruvian historians such as Jorge Basadre and Gustavo Pons Muzzo agree that the Salomón-Lozano Treaty was an error in Leguía's diplomacy, considering that Colombia came out with a greater advantage in the territorial cession and that Peru renounced a policy of defense of its territory that it had maintained until then unchanged.[90]​[88]​ This interpretation is the one that has been perpetuated in Peruvian teaching and the one that has given rise to the black legend of Leguía. On the other hand, in Colombia it is considered that it was a transactional agreement, that is, that both parties renounced their maximum claims, made mutual concessions and reached a balanced agreement.

Leguía also proposed to definitively resolve the problem with Chile regarding the question of Tacna and Arica. As the years passed, the plebiscite initially agreed upon in the Treaty of Ancón of 1883 to decide the fate of the Peruvian provinces of Tacna and Arica, held captive in Chile since the Pacific War of 1879-1883, became unattainable.[91]​.

When the dispute was submitted to the arbitration of the President of the United States Calvin Coolidge, he gave his ruling (award) on March 4, 1925, resolving to hold the plebiscite. This award was not well received by Peruvian public opinion, too aware of Chile's behavior towards these provinces, which it had subjected to a heartless policy of "Chileanization" for many years. Indeed, the American commissioners who came to supervise the plebiscite, Generals John J. Pershing and William Lassiter, verified that it was impracticable due to the lack of minimum conditions for a fair and objective popular consultation.[92]​[93]​.

The plebiscite did not take place and both parties returned to direct negotiations, which culminated in the treaty signed on June 3, 1929, in Lima, between the Peruvian chancellor Pedro José Rada y Gamio and the Chilean representative Emiliano Figueroa Larraín (which is why it is also known as the Rada y Gamio-Figueroa Larraín Treaty). Both parties definitively renounced the holding of the plebiscite with the following arrangement: Tacna would return to the heart of the Peruvian homeland, but Chile would remain with Arica. In addition, other concessions were granted to Peru in Arica, such as a dock and its customs infrastructure, possession of the House of Response, possession of the Tacna-Arica railway station and the route of its line, the water sources of the Uchusuma and Maure, among other easements.[94][95]​.

On August 28, 1929, Tacna was reincorporated into Peru.

The world crisis of 1929 had very serious effects on the national economy of Peru. The working sectors, directly affected by the rise in the cost of living and the scarcity of subsistence, were the first to raise their protest. The army also showed its discontent. The evident administrative corruption, from which close associates or friends of the president benefited throughout the regime, as well as the signing of treaties with Colombia and Chile with territorial transfer, further accentuated opposition to the government. Subversive actions and assassination attempts on the president were rumored.

On August 22, 1930, Commander Luis Miguel Sánchez Cerro, in command of the Arequipa garrison, spoke out against the government. The revolutionary movement spread quickly through the south of the country. Also in Lima the atmosphere was favorable for the revolution. To dominate the situation, Leguía attempted to form a military cabinet, but in the early hours of the morning on August 25, the Lima garrison requested his resignation.[99]​.

Leguía accepted and resigned command, which remained in the hands of a Military Government Junta chaired by General Manuel María Ponce Brousset.[100]​ Two days later he would hand over power to Sánchez Cerro, who arrived in the capital by plane.[101]​.