British-Israelism

"Foremost among these external anti-Semitic motifs brought into British-Israelism was the charge that Eastern European Jews were in fact not europeans at all but were "Asiatics". The specific form this took twas the accusation that Jews from the czar's empire were descendents of the Khazars, a people that had once lived near the shores of the Black Sea, and whose leadership stratum and an unknown portion of its populace had converted to Judaism in the seventh century. The Khazar theory never figured as a major component of anti-Semitism. Indeed, it only receives scant attention in Leon Poliakov's monumental history of the subject. However, it came to exercise a particular attraction for the advocates of immigration restriction in America. Since they had a well-developed position on the exclusion of "Orientals", particularly the Chinese, the suggestion that Jews were Asiatics rather than Europeans made it possible to include them within an existing category of inadmissible foreigners. Hence, in the 1920s, when immigration restrictionism reached a peak, the Khazar theory enjoyed a vogue in America, although it had in fact existed for several decades before that.

The earliest suggestion that Khazar ancestry played a significant role in determining the composition of Ashkenazic Jewry appears to have been in a lecture given by Ernest Renan, "Judaism as a Race and as a Religion," on January 27, 1883. Although the conversion of the Khazar ruling group was well known, Renan seems to have been the first to suggest that Khazar converts may have been numerous enough to constitute a major proportion of East European Jewry. Renan's suggestion was consistent with his long-standing belief that a racial distinction separated Jews from Aryans. There was, however, no immediate reason for such a view to exercise an attraction for British-Israelites, except insofar as they might, for their own reasons, have harboured an antipathy towards Ashkenazic Jews. There was nothing in the Khazar theory per se that commended it to British-Israelites, for - ironically - legend had for generations associated the Black Sea Khazars with the ten lost tribes of Israel.
(Barkun, M., 1997 (Revised Edition): Religion and the Racist Right - The Origins of Christian Identity Movement -- Chapter 7:The Demonisation of Jews I:Racial Anti-Semitism -- Jews as Asiatics: The Khazar Hypothesis pp.136-142)