The Rus' warlords launched several wars against the Khazar Qağanate, and raided down to the Caspian sea. The Schechter Letter relates the story of a campaign against Khazaria by HLGW (recently identified as Oleg of Chernigov) around 941 in which Oleg was defeated by the Khazar general Pesakh. The Khazar alliance with the Byzantine empire began to collapse in the early 10th century. Byzantine and Khazar forces may have clashed in the Crimea, and by the 940s emperor Constantine VII Porphyrogenitus was speculating in De Administrando Imperio about ways in which the Khazars could be isolated and attacked. The Byzantines during the same period began to attempt alliances with the Pechenegs and the Rus', with varying degrees of success. Sviatoslav I finally succeeded in destroying Khazar imperial power in the 960s, in a circular sweep that overwhelmed Khazar fortresses like Sarkel and Tamatarkha, and reached as far as the Caucasian Kassogians/Circassians and then back to Kyiv. Sarkel fell in 965, with the capital city of Atil following, c. 968 or 969. Thus, the Kievan Rus' would dominate the north-south trade routes through the steppe and across the Black Sea.
Although Poliak argued that the Khazar kingdom did not wholly succumb to Sviatoslav's campaign, but lingered on until 1224, when the Mongols invaded Rus', by most accounts, the Rus'-Oghuz campaigns left Khazaria devastated, with perhaps many Khazarian Jews in flight, and leaving behind at best a minor rump state. It left little trace, except for some placenames, and much of its population was undoubtedly absorbed in successor hordes.