Since 1913, however, an extensive diamond field in the Kasai basin along the Angola border has been worked.
From the tableland the Kwango and many other streams flow north to join the Kasai (one of the largest affluents of the Congo), which in its upper course forms for fully 300 m.
In the central Kasai region the state had been unable to make its authority good up to the time it ceased to exist.
The American Congo Company was granted a rubber concession in the Kasai basin.
Extending from the Kwango affluent of the Kasai to Lake Tanganyika are the Luba-Lunda groups.
Living north of the Luba-Lunda tribes, and occupying the country enclosed by the great bend of the Congo and bounded west by the Kasai, are a large number of tribes, the chief groups being the Bakuba, Basongo Mino, Balolo, Bakete, Bambala, Bayaka, Bahuana, &c. Of these the Basongo Mino are spread over the country between the Kasai and Lomami.
Along the middle Congo from Stanley Pool to Stanley Falls the more important tribes are the Bateke, in the Stanley Pool district, but chiefly on the north side of the river in French territory; the Bayanzi (Babangi), between the mouths of the Kasai and the Ubangi; the Bangala, one of the most gifted of the Congo tribes, whence are recruited many of the soldiery; the Bapoto and the Basoko.
Yanvo fell to pieces on the death of the chief Muteba, killed in a war with the Kioke, a Bantu tribe of the upper Kasai, in 1892.
Later on a chief named Kalambo carved out a new" empire in the central part of the Kasai basin, his authority extending westward from the upper Sankuru into the Lunda district of Angola.
Other places of importance are Luluaburg, on the Lulua river; Lusambo, the capital of the Lualaba-Kasai district, on the Sankuru river; Coquilhatville, the capital of the equatorial district, at the mouth of the Ruki; Stanleyville, the principal station of Stanley Falls district; New Antwerp, a thriving little town, the capital of the Bangala district, situated on the right bank of the Congo close to 19° E.; Banzyville, the capital of the Ubangi district, on the river of that name; and Basoko, at the junction of the Aruwimi and the Congo.
It has been found in the Manyanga country, the Manyema country on the upper Congo, in the Urua country, in the basins of the Kasai and the Lualaba, and in Katanga.
North of these, in the great bend of the Congo, are the Balolo, &c., the Balolo a nation of iron-workers; and westward, on the Kasai, the Bakuba, and a large number of tribes as yet imperfectly known.
Forestry and mining are both undeveloped, but the syndicate which since 1908 has worked the Kasai diamond area of the Belgian Congo has also concessions on the Portuguese side, and in 1920 the output of diamonds from Angola was estimated at 120,000 carats.
The districts are Banana, Boma, Matadi, Falls, Stanley Pool, Kwango Oriental, Ubangi, Lualaba-Kasai, Lake Leopold II., Equator, Aruwimi, Bangala and Welle.