The Thirteenth Tribe: The Khazar Empire and its Heritage

The 'Khazar origin' of modern Jewry theory - disproven by Mourant's "The Genetics of the Jews" (1978) based on hematological studies. Possible reasons for Koestler's book briefly addressed in "Jacob's Legacy" (2008)(GOLDSTEIN, David B.).
'This is an absorbing account of the ancient Khazar Empire... and the close and unexpected bearing it has on our world today. In the Middle Ages, the Khazars’ sway extended from the Black Sea to the Caspian, from the Caucasus to the Volga. But they found themselves in a precarious position between two major world powers: the Eastern Roman Empire and the triumphant followers of Mohammed. The Khazars were the Third Force of their day, and they chose a surprising method of resisting pressure from both Christianity and Islam: they converted to Judaism. In the second part of the book, Koestler speculates about the ultimate faith of the Khazars and their impact on the racial composition and social heritage of modern Jewry. He produces detailed research to support a theory which could make the term ‘anti-Semitism’ become void of meaning.'--back cover blurb