The Khazars (Eastern Europeans) evidently converted to Judaism around 740 A.D. as an opportunistic way to maintain independance from, and a measure of peaceful relations with, the Islamic Turks to the Southeast and the Christians (Byzantine) to the Northwest...

Their own documents (if accurate) trace their ancestry through Ashkenaz to Japheth...

Which also means they're of the line of Gomer and so related more closely to the Gernanic family line that to the actual Semites...what a mess...

[[ Interesting anecdote, this explains why my in-laws who are of Polish-Ukrainian descent have Ashkenazi blood markers--I'd always been confused by that but only out of ignorance. ]]

I'm about halfway done with Koestler, might read Schlomo Sand next.