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.