Treaty of Ancón

The Treaty of Ancón was signed by Peru and Chile on 20 October 1883, in the Ancón District near Lima. It was intended to settle the two nations' remaining territorial differences at the conclusion of their involvement in the War of the Pacific and to stabilise post-bellum relations between them.

Under the treaty's terms, Chile gained control over the province of Tarapacá. Chile was also to occupy the provinces of Tacna and Arica for ten years, after which a plebiscite would be organised to determine their nationality. However, for several decades following the two countries were unable to reach agreement on the terms the plebiscite.

Finally, in 1929, through the mediation of the United States under President Herbert Hoover, an accord was reached. Under the Tacna-Arica compromise, Chile kept Arica, while Peru reacquired Tacna and received USD $6 million indemnity and other concessions.

Another important chapter in the treaty said that Chile could not give sovereignty of former Peruvian territories to other nations without asking Peru first. The Chapter have been invoked once, during the Chilean proposal of 1975 that offered Bolivia sovereignty over some minor ports.