 In English, "Cossack" is first attested in 1590.It is unclear when Slavic people other than the Brodnici and Berladniki began to settle in the lower reaches of major rivers such as the Don and the Dnieper after the demise of the Khazar state.Their arrival is unlikely before the 13th century, when the Mongols broke the power of the Cumans, who had assimilated the previous population on that territory.