The history of the ancient Khazar Empire, a major but almost forgotten power in Eastern Europe, which in A.D. 740 converted to Judaism. Khazaria, a conglomerate of Aryan Turkic tribes, was finally wiped out by the forces of Genghis Khan, but evidence indicates that the Khazars themselves migrated to Poland and formed the cradle of Western (Ashkenazim) Jewry...
The Khazars' sway extended from the Black sea to the Caspian, from the Caucasus to the Volga, and they were instrumental in stopping the Muslim onslaught against Byzantium, the eastern jaw of the gigantic pincer movement that in the West swept across northern Africa and into Spain.
Thereafter the Khazars found themselves in a precarious position between the two major world powers: the Eastern Roman Empire in Byzantium and the triumphant followers of Mohammed.
As Arthur Koestler points out, the Khazars were the Third World of their day, and they chose a surprising method of resisting both the Western pressure to become Christian and the Eastern to adopt Islam. Rejecting both, they converted to Judaism.