In 1975 Spain relinquished its claim to Spanish Sahara in northwest Africa and in early 1976 the territory, since known as Western Sahara, was divided between Morocco and Mauritania, with Morocco receiving about two thirds of the area. At the same time the Polisario Front, backed by Algeria and Libya, proclaimed the independence of the territory under principles of self-determination. The chief economic asset of the area is rich phosphate deposits.
For a time the Polisario guerrillas were fighting in a three-way war involving both Morocco and Mauritania, but in 1978 the Mauritanian government agreed to a cease-fire with the Polisario, and the following year withdrew from Western Sahara in favor of Polisario claims to legitimacy there. Since that time the Polisario forces have enjoyed sanctuary in Algeria and Mauritania in addition to their control of desert areas within Western Sahara.