According to an article published at the World Zionist Organization's (WZO) website:
"REMARKABLY, the Khazars, a people of Turkic origin, converted to the Jewish religion sometime in the 9th century, beginning with the royal house and spreading gradually among the general populace. Judaism is now known to have been more widespread among the Khazar inhabitants of the Khazar kingdom than was previously thought. In 1999, Russian archaeologists announced that they had successfully reconstructed a Khazarian vessel from the Don River region, revealing 4 inscriptions of the word "Israel" in Hebrew lettering. It is now the accepted opinion among most scholars in the field that the conversion of the Khazars to Judaism was widespread, and not limited merely to the royal house and nobility. Ibn al-Faqih, in fact, wrote "All of the Khazars are Jews." Christian of Stavelot wrote in 864 that "all of them profess the Jewish faith in its entirety." Click here to view the full article and links to the original sources (saved at archive.org); Do you wonder why WZO deleted it?
Source: Atlas of World History, p. 108