The Khazar hypothesis is the claim that Ashkenazi Jews - the historically European-based Jewish population - are primarily descended not from ancient Israelites but from the Khazars, a Turkic people whose ruling class is documented in several medieval sources to have converted to Judaism in the early medieval period. The hypothesis carries political implications beyond its historical and genetic dimensions, as some versions of it are used to argue that Ashkenazi Jews have no ancestral connection to the Levant and therefore no legitimate claim to the land of Israel. The topic intersects archaeology, medieval history, population genetics, and contemporary geopolitics.
The Khazars were a semi-nomadic Turkic people who dominated the Pontic steppe and the Caucasus region roughly from the 7th to the 10th century CE, operating a powerful empire centered north of the Caucasus Mountains between the Black Sea and the Caspian Sea. Historical sources - including correspondence attributed to the Khazar ruler Joseph and accounts from Arab, Byzantine, and Hebrew chroniclers - document that the Khazar elite converted to Judaism, likely in the 8th or 9th century CE, though the reliability of these sources has been questioned by some scholars.(7) The extent to which this conversion spread beyond the ruling class, and what ultimately became of the Khazar population after the empire's collapse in the late 10th century, are both contested. For a fuller treatment, see Khazar Hypothesis - History.
The modern form of the hypothesis was most prominently advanced by Arthur Koestler in his 1976 book The Thirteenth Tribe, which argued that the bulk of Ashkenazi Jewry descends from Khazar converts rather than from Israelite diaspora communities.(1) The hypothesis has since been taken up by various scholars and non-scholars with differing motivations and varying degrees of rigor.
Population genetics has become the dominant framework within which the hypothesis is evaluated. The prevailing view in the genetics literature is that Ashkenazi Jews show substantial genomic affinities with populations from the ancient Near East - particularly with other Jewish diaspora communities and with Levantine populations - while also showing significant European admixture, consistent with a history of settlement and intermarriage in European host populations.(2)(3)
Critics of the hypothesis argue that the genetic, archaeological, and documentary evidence does not support a mass Khazar origin for Ashkenazi Jews.(2)(3)(5)(6)
Defenders of the hypothesis, including Israeli scholar Eran Elhaik, argue that certain genetic analyses do show signatures consistent with a Khazar or broader Caucasian contribution to Ashkenazi ancestry, and that the mainstream interpretation of the genetic data is influenced by prior assumptions. Elhaik's 2012 paper in Genome Biology and Evolution argued that Ashkenazi Jews cluster genetically closer to Caucasian and Iranian populations than the prevailing consensus holds.(4) For a full treatment of the competing arguments, see Khazar Hypothesis - Debate.
The mainstream consensus in both genetics and medieval history holds that Ashkenazi Jews are primarily of ancient Israelite descent with significant European admixture, and that Khazar ancestry, if present at all, is a minor component. See Khazar Hypothesis - Genetics Consensus and Khazar Hypothesis - History Consensus.