Monograph by A.N. Usmanov, published in 1960, is one of the first generalizing studies of the processes of entry of Bashkir tribes into the Russian state. Against a wide historical background, the author reveals the socio-economic and socio-cultural aspects of the accession of the Bashkir tribes, which were in the 16th century depending on the Kazan Khanate, the Siberian Khanate and the Nogai Horde. The features of the acceptance of citizenship by various Bashkir tribes are revealed. The book also contains sections on the management of Bashkiria after accession, the founding of the city of Ufa, the beginning of the economic development of the region (XVI-XVII centuries). The study of A.N. Usmanov has important historiographic significance, being a classic example of the concept of "voluntary accession" of non-Russian nationalities to Russia.