I was reading a few articles on the Khazar hypothesis and had a couple of thoughts:
It's interesting how the popularity of myths wax and wane depending on their contemporary ramifications.
When I was a kid, the idea that there was an early medieval kingdom that converted entirely to Judaism was something that was embraced by the Orthodox Jewish community. It was empowering, exciting, and something to be proud of.
However, that's changed in recent years. Given that Shlomo Sand and others have used the legend as the basis of their theories that most of Ashkenazic Jewry is descended from the Khazars, and not of ancient Judeans, it's become highly politicized. Now it's become much more fashionable in the Orthodox Jewish community to reject the conversion as a myth, to avoid giving ammunition to those who would undermine the Jewish claim to Israel.
I suspect that the myth would have stayed that way, a myth, along with many other medieval myths, had R Yehuda Halevi not used it as the backdrop to his fictional philosophical dialogue in the Kuzari.