By the 9th century, groups of Varangian Rus', developing a powerful warrior-merchant system, began probing south down the waterways controlled by the Khazars and their protectorate, the Volga Bulgarians, partially in pursuit of the Arab silver that flowed north for hoarding through the Khazarian-Volga Bulgarian trading zones, partially to trade in furs and ironwork.
Northern mercantile fleets passing Atil were tithed, as they were at Byzantine Cherson.
Their presence may have prompted the formation of a Rus' state by convincing the Slavs, Merja and the Chud' to unite to protect common interests against Khazarian exactions of tribute.
It is often argued that a Rus' Khaganate modelled on the Khazarian state had formed to the east, and that the Varangian chieftain of the coalition appropriated the title of qağan (khagan) as early as the 830s: the title survived to denote the princes of Kievan Rus', whose capital, Kiev, is often associated with a Khazarian foundation.
The construction of the Sarkel fortress, with technical assistance from Khazaria's Byzantine ally at the time, together with the minting of an autonomous Khazar coinage around the 830s, may have been a defensive measure against emerging threats from Varangians to the north and from the Magyars on the eastern steppe.
By 860, the Rus' had penetrated as far as Kiev and, via the Dnieper, Constantinople.

Alliances often shifted.
Byzantium, threatened by Varangian Rus' raiders, would assist Khazaria, and Khazaria at times allowed the northerners to pass through their territory in exchange for a portion of the booty.
From the beginning of the 10th century, the Khazars found themselves fighting on multiple fronts as nomadic incursions were exacerbated by uprisings by former clients and invasions from former allies.
The pax Khazarica was caught in a pincer movement between steppe Pechenegs and the strengthening of an emergent Rus' power to the north, both undermining Khazaria's tributary empire.
According to the Schechter Text, the Khazar ruler King Benjamin (ca.880–890) fought a battle against the allied forces of five lands whose moves were perhaps encouraged by Byzantium.
Although Benjamin was victorious, his son Aaron II faced another invasion, this time led by the Alans, whose leader had converted to Christianity and entered into an alliance with Byzantium, which, under Leo VI the Wise, encouraged them to fight against the Khazars.

By the 880s, Khazar control of the Middle Dnieper from Kiev, where they collected tribute from Eastern Slavic tribes, began to wane as Oleg of Novgorod wrested control of the city from the Varangian warlords Askold and Dir, and embarked on what was to prove to be the foundation of a Rus' empire.
The Khazars had initially allowed the Rus' to use the trade route along the Volga River, and raid southwards.
See Caspian expeditions of the Rus'.
According to Al-Mas'udi, the qağan is said to have given his assent on the condition that the Rus' give him half of the booty.
In 913, however, two years after Byzantium concluded a peace treaty with the Rus' in 911, a Varangian foray, with Khazar connivance, through Arab lands led to a request to the Khazar throne by the Khwârazmian Islamic guard for permission to retaliate against the large Rus' contingent on its return.
The purpose was to revenge the violence the Rus' razzias had inflicted on their fellow Muslim believers.
The Rus' force was thoroughly routed and massacred.
The Khazar rulers closed the passage down the Volga to the Rus', sparking a war.
In the early 960s, Khazar ruler Joseph wrote to Hasdai ibn Shaprut about the deterioration of Khazar relations with the Rus': 'I protect the mouth of the river (Itil-Volga) and prevent the Rus arriving in their ships from setting off by sea against the Ishmaelites and (equally) all (their) enemies from setting off by land to Bab.'

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 Chernigo
By the 9th century, groups of Varangian Rus', developing a powerful warrior-merchant system, began probing south down the waterways controlled by the Khazars and their protectorate, the Volga Bulgarians, partially in pursuit of the Arab silver that flowed north for hoarding through the Khazarian-Volga Bulgarian trading zones, partially to trade in furs and ironwork. Northern mercantile fleets passing Atil were tithed, as they were at Byzantine Cherson. Their presence may have prompted the formation of a Rus' state by convincing the Slavs, Merja and the Chud' to unite to protect common interests against Khazarian exactions of tribute. It is often argued that a Rus' Khaganate modelled on the Khazarian state had formed to the east, and that the Varangian chieftain of the coalition appropriated the title of qağan (khagan) as early as the 830s: the title survived to denote the princes of Kievan Rus', whose capital, Kiev, is often associated with a Khazarian foundation. The construction of the Sarkel fortress, with technical assistance from Khazaria's Byzantine ally at the time, together with the minting of an autonomous Khazar coinage around the 830s, may have been a defensive measure against emerging threats from Varangians to the north and from the Magyars on the eastern steppe. By 860, the Rus' had penetrated as far as Kiev and, via the Dnieper, Constantinople.
Alliances often shifted. Byzantium, threatened by Varangian Rus' raiders, would assist Khazaria, and Khazaria at times allowed the northerners to pass through their territory in exchange for a portion of the booty. From the beginning of the 10th century, the Khazars found themselves fighting on multiple fronts as nomadic incursions were exacerbated by uprisings by former clients and invasions from former allies. The pax Khazarica was caught in a pincer movement between steppe Pechenegs and the strengthening of an emergent Rus' power to the north, both undermining Khazaria's tributary empire. According to the Schechter Text, the Khazar ruler King Benjamin (ca.880–890) fought a battle against the allied forces of five lands whose moves were perhaps encouraged by Byzantium. Although Benjamin was victorious, his son Aaron II faced another invasion, this time led by the Alans, whose leader had converted to Christianity and entered into an alliance with Byzantium, which, under Leo VI the Wise, encouraged them to fight against the Khazars.
By the 880s, Khazar control of the Middle Dnieper from Kiev, where they collected tribute from Eastern Slavic tribes, began to wane as Oleg of Novgorod wrested control of the city from the Varangian warlords Askold and Dir, and embarked on what was to prove to be the foundation of a Rus' empire. The Khazars had initially allowed the Rus' to use the trade route along the Volga River, and raid southwards. See Caspian expeditions of the Rus'. According to Al-Mas'udi, the qağan is said to have given his assent on the condition that the Rus' give him half of the booty. In 913, however, two years after Byzantium concluded a peace treaty with the Rus' in 911, a Varangian foray, with Khazar connivance, through Arab lands led to a request to the Khazar throne by the Khwârazmian Islamic guard for permission to retaliate against the large Rus' contingent on its return. The purpose was to revenge the violence the Rus' razzias had inflicted on their fellow Muslim believers. The Rus' force was thoroughly routed and massacred. The Khazar rulers closed the passage down the Volga to the Rus', sparking a war. In the early 960s, Khazar ruler Joseph wrote to Hasdai ibn Shaprut about the deterioration of Khazar relations with the Rus': 'I protect the mouth of the river (Itil-Volga) and prevent the Rus arriving in their ships from setting off by sea against the Ishmaelites and (equally) all (their) enemies from setting off by land to Bab.'
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 Chernigo
Khazars