At some point in the 19th century, a number of scholars tried to trace the lineage of East European Jewry not to German Jews who settled there in the late medieval period but to the survivors of the Khazar empire, which ruled over a large area in what is now eastern Ukraine and southwest Russia in the 8th through 10th centuries CE. This hypothesis, popularized by the Hungarian-British writer Arthur Koestler in the 1970s, claims that the Turkic-speaking Khazars converted to Judaism en masse and, after their empire was destroyed, settled throughout Poland, Ukraine, and Belarus, where their descendants came to constitute the bulk of the Jewish population. From this it allegedly follows that most modern Ashkenazim are unrelated to biblical Israelites, and that the historical Jewish connection to the land of Israel is attenuated if not false. Long discredited, the theory has recently been revived by a handful of academics. But the evidence against it is greater than ever, as the linguist and onomastician Alexander Beider explains:
[A]rchaeological evidence about the widespread existence of Jews in Khazaria is almost nonexistent. While a series of independent sources does testify to the existence in the 10th century of Jews in the kingdom of Khazaria, and while some of these sources also indicate that the ruling elite of Khazaria embraced Judaism, . . . we can be confident that Judaism was not particularly widespread in that kingdom.
The next historical record of Jews [in the region]—in a few cities that today belong to western Ukraine and western Belarus—shows up in the 14th century, when Jews are regularly referred to in numerous documents. And yet, no direct historiographical data are available to connect the Jews who lived in Eastern Europe in the 14th century with their coreligionists from 10th-century Khazaria. . . .
Looking at names, both first names and surnames, gives us a sense of how a community would see itself, its language, and its origins. And in the Jewish communities of Eastern Europe over the past six centuries, not a single Turkic name can be found in documents listing Jewish names. Even documents from the 15th and 16th centuries dealing with Jews who lived in the territories of modern Ukraine and Belarus have no such names.
In the corpus of given names used by Jews of Eastern Europe during the last centuries, we find the same linguistic layers as in the lexicon of Yiddish. There are numerous Germanic and Hebrew names and some Aramaic names. There are also Greek names (Todros from Theodoros, Kalmen from Kalonymos), Old French names (Beyle, Bunem, Yentl), Old Czech names (Khlavne, Slave, Zlate), and Polish names (Basye, Tsile), and very few East Slavic [i.e., Belarusian, Ukrainian, or Russian] names (Badane, Vikhne). There are no Turkic names. . . .
Globally speaking, all arguments suggested by proponents of the Khazarian theory are either highly speculative or simply wrong. They cannot be taken seriously. This has never stopped the theory from being popular. The ideological reasons for this are material for another occasion.