Chilean–Peruvian territorial dispute

The Chilean–Peruvian territorial dispute was 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 settled maritime dispute between both states.

The Treaty of Ancón, which put an end to the War of the Pacific, was signed on October 20, 1883. The following year, Chile formally incorporated the former Peruvian provinces of Tacna, Arica and Tarata into a province on October 31, the latter of which would be constested due to differing interpretations of the course of the Sama River, the provisional border. Under the treaty, the territory would be administered by Chile for a ten-year period, after which a plebiscite would determine its fate. Originally meant to be held in 1894, was ultimately not carried out.

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 pursued an acculturation policy that saw the establishment of Chilean culture and a Chilean population in the region. 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.

The dispute continued into 1929, ending through the signing of the Treaty of Lima, under which Tacna would be returned to Peru, while Arica would be formally incorporated into Chile. The handover of Tacna took place at midnight on August 28, 1929, marking the end of the Chilean administration. Following the main dispute's resolution, a minor continuation would evolve into an international law case concerning a disputed maritime zone between both states. The International Court of Justice judged in favour of Peru in 2014, after which a 37,610 km² territory immediately east of the Pacific Ocean has become the only unresolved aspect of the dispute as a whole.