The hypothesis of this brief but startling study is that the majority of Eastern European Jews did not originally come from France and Western Germany, but from the dispersion of the Khazar empire around the 12th century. The Khazars evidently originated on the Asian steppes, spoke a Turkish language, and adopted Judaism in the 8th century. They could afford the conversion, writes Koestler, because of their economic and military strength, based on Caucasian natural resources; and they kept the Arabs from invading Byzantium, a service finally rewarded by an 11th century Russo-Byzantine alliance against their own empire, whose survivors moved into Hungary, Poland, Lithuania, and the Ukraine. As a supplementary argument for the Khazar origins of Eastern European Jewry, the book calculates that the extermination of Western Jewish settlements left too few migrants to execute the often-assumed ""mass exodus"" across Germany. Koestler suggests that if his theory is correct and most Jews are not descended from Biblical tribes, ""then the term 'anti-Semitism' would become void of meaning, based on a misapprehension shared by both the killers and their victims."" More to the point, Koestler ends with a summary of genetic studies by Raphael Patai and others suggesting that not only were Biblical Jews a ""hybrid"" population (as were the Khazars), but no ""Jewish race"" can be scientifically identified. Certain to draw attention, this is no great shocker but a modest, detached investigation.