Local populations of the Caucasus including the Circassians long practiced various forms of servitude and slave trading. In the nineteenth century, many inhabitants of the Caucasus, especially Christian Georgians and Armenians and heterodox Muslim Circassians were sent as slaves to the Ottoman Empire. The Ottomans imported between 16.000 and 18.000 such slaves every year. Moreover, the brutal Russian conquest of Circassia (finished on 2 June 1864) led to an influx of between half a million and a million refugees into the Ottoman domains, of whom perhaps a tenth were of servile status. These massive arrivals increased the number of agricultural slaves in the Ottoman Empire.
Read more? Alessandro Stanziani, Bondage. Labor and Rights in Eurasia from the 16th to the early 20th centuries (New York 2014)