The Thirteenth Tribe (English Edition)

In this book. Arthur Koestler advances the thesis that Ashkenazi Jews are not descended from the historical Israelites of antiquity, but from Khazars, a Turkic people. Koestler's hypothesis is that the Khazars converted to Judaism in the 8th century, and migrated westwards into Eastern Europe in the 12th and 13th centuries when the Khazar Empire was collapsing.