Why Chile is so long and thin

Between the mountains and the sea

Chile runs about 4,300 km from its border with Peru to Cape Horn, only about 400 miles (640 km) north of Antarctica. It averages about 177 km wide, is at its widest (349 km) at the latitude of Antofagasta, and is only about 15 km across near Puerto Natales.^[1] The Andes run along its eastern side and the Pacific along its western side.^[1]

The colony that became Chile grew up in between. At the end of Spanish rule most of its people lived in the Aconcagua Valley and the Central Valley from Santiago to Concepción, which Britannica calls “the cradle of Chilean nationality.”^[6]

A line along the highest peaks

Chile and Argentina first agreed their border in a treaty of 30 August 1855, which kept the colonial line as it stood in 1810. A treaty of 1881 set the border along the main range of the Andes as far south as latitude 52° S.^[2] A protocol of 1 May 1893 gave Argentina everything east of “the line of the highest peaks which divide the waters” and Chile everything west of it.^[2]

That wording assumed the highest peaks and the water divide were the same line. In high mountains the two lines often part, and the countries ended up disagreeing over four stretches.^[2] They asked the British Crown to arbitrate. In its award of 20 November 1902 King Edward VII gave Argentina the upper basins of several disputed rivers and Chile the lower basins.^[2] One sector, Palena, went back to British arbitration, and a 1966 award gave about 30% of the disputed land to Chile and the rest to Argentina.^[2]

“hold in perpetuity all territory to the east of the line of the highest peaks which divide the waters while Chile was to hold in perpetuity all territory to the west of that line.”^[2]

The desert war

When Bolivia became independent in 1825 it claimed a stretch of Pacific coast across part of the Atacama Desert, between the Salado River and the Loa River.^[3] Chile began claiming the desert in 1842, after nitrate deposits were found there. A treaty of 10 August 1866 made the 24th parallel the border.^[3]

In 1878 Bolivia put a tax on a nitrate company that had passed into Chilean hands, which broke a promise in the 1866 treaty. Chile occupied part of Bolivia’s coast in February 1879, and on 5 April 1879 it declared war on both Bolivia and Peru, which had a defensive alliance.^[3] Chile won and annexed the nitrate provinces.^[4]

In the Treaty of Ancón of 20 October 1883, Peru ceded Tarapacá to Chile outright.^[3] Bolivia signed a truce in 1884 and, in a peace treaty of 20 October 1904, recognised Chile’s sovereignty over its former coast. In return Chile granted Bolivia commercial transit through its territory and ports, in perpetuity.^[3]

Tacna and Arica

The Treaty of Ancón also let Chile run the Peruvian provinces of Tacna and Arica for ten years, after which a vote would decide their future. The two sides never agreed how to hold it, and Chile stayed.^[5] In 1925 US President Calvin Coolidge ruled that a plebiscite should go ahead, but attempts to organise it were suspended in 1926.^[5]

After President Herbert Hoover proposed terms in May 1929, the two countries signed a treaty at Lima on 3 June 1929 that split the territory: Tacna went to Peru and Arica to Chile.^[5] The resulting border is about 106 miles (171 km) long and was marked with pillars by 1930.^[5]