For background see Russian conquest of the Caucasus. Around 1560 Russia interacted with Kabardia but thereafter left the region alone except for the Caspian coast. In 1800 Russia annexed eastern Georgia and by 1806 held Transcaucasia from the Black Sea to the Caspian. Since Russia also claimed the steppes north of the mountains its claims were divided by the free mountaineers of the Caucasus. Russia had to hold the Georgian Military Highway in the center so the war against the mountaineers was divided into eastern and western parts. Circassia  refers to a region the majority of whose inhabitants before the 1860s were the Adygey  ethnic group, known to the West as Circassians. This region consisted for the most part of the region between the westward flowing Kuban River to the north and the Caucasus mountain range to the south, although the Kuban River constituted only part of the northern boundary. The Circassians were never politically united for a long period. The western bulk of Circassia, they belonged to any of about ten tribes, living in communities headed by chieftains. In the east of Circassia were two feudal polities, Greater Kabardá and Lesser Kabardá. In the late 1550s, the ruler of one of the Kabardás, Temryuk , struck a politico-military alliance with Tsar Ivan IV of Russia , for mutual assistance against expansionist attacks by the Persian and Ottoman Empires. In this period of history, the Circassians were Christians; Islam did not begin to penetrate Circassia until the following century. In the 1560s Ivan and Temryuk directed forts to be constructed, including Tumnev at the western end of Circassian lands and at Sunzha Ostrog at the mouth of the Sunzha river, at the eastern end of Circassian lands.. Which region is between the westward flowing Kuban River to the north and the Caucasus mountain range to the south?