The Chilean–Peruvian territorial dispute is a territorial dispute between Chile and Peru that started in the aftermath of the War of the Pacific and ended significantly in 1929 with the signing of the Treaty of Lima and in 2014 with a ruling by the International Court of Justice. The dispute applies since 2014 to a 37,610 km2 territory in the Chile–Peru border, as a result of the maritime dispute between both states.
Background
Unlike other South American border conflicts, after the Chilean and Peruvian wars of independence, both countries did not share a border until 1883 due to Bolivia's Litoral Department. With the War of the Pacific beginning in 1879, the Chilean land and naval campaigns saw quick success, with the war ending with Peru signing the Treaty of Ancón in 1883, and Bolivia signing the Treaty of Valparaiso the following year. As a result of the former treaty, Peru ceded its Tarapacá Department and established a new border with Chile, while the Chilean government administered the territories of Tacna and Arica under the newly established Tacna Province until a plebiscite could be held in 1894. From 1890 to 1929, Locumba served as the provisional capital of the area of the Department of Tacna not under Chilean administration, which came to be known as Free Tacna ().
Tacna and Arica dispute
In the aftermath of the signing of the Treaty of Ancón, the Department of Tarapacá was unconditionally ceded to Chile, being replaced by Tarapacá Province, and the provinces of Tacna and Arica were placed under the administration of the new Tacna Province. As per the treaty, a plebiscite was to be held in 1894, which would determine the fate of the province. The plebiscite, however, was never carried out. During this time, the term Captive provinces () was used to refer to Tacna and Arica.
During the early years of the post-war era, the Chilean and Peruvian governments exercised extensive campaigns to solidify their control over the region. On one hand, Peru established a campaign of foreign support, which attracted the attention of the United States as a mediator in the conflict. On the other hand, Chile established a campaign of acculturation known as Chilenization, which saw the establishment of Chilean culture and a Chilean population in the region. One legacy of Chilean presence in Tacna was the Tacna Prefecture, the building where the intendant resided. Local Peruvian loyalists also established resistance movements, which saw armed combat on at least one occasion. To counter this and to incite an exodus of Peruvians that remained in the area, groups known as Patriotic Leagues were established.
Tarata Department
In 1885, the Department of Tarata was established by Chile as a subdivision of Tacna Province. The creation of the Department caused controversy in Peru, due to both countries disagreeing on their border in the Sama river. While the Chilean government argued the town was to the east of the river, the border agreed upon by both countries, Peru disputed this claim on the grounds that the territory was not affected by the Treaty of Ancón and established a policy of non-recognition. Around this time, there were claims of military escalation, including claims of Peruvian troops mobilizing near the Chilean border, which were denied by the Peruvian government.
The Department was abolished under Arturo Alessandri's administration by law № 3,802 on September 22, 1921. On September 1, 1925, at exactly 10 am, Chile handed over the former Department to Peru in a ceremony that took place in the main square, with representatives from both countries present: with representing Chile, Manuel de Freyre y Santander representing Peru, and General Pershing representing the United States.