Wikipedia
The Khazars (,, (Kuzarim), (khazar), , , , , ) were a semi- nomadic Turkic people, who created what for its duration was the most powerful polity to emerge from the breakup of the western Turkish steppe empire, known as the Khazar Khanate or Khazaria. Astride a major artery of commerce between northern Europe and southwestern Asia, Khazaria became one of the foremost trading emporia of the medieval world, commanding the western marches of the Silk Road and playing a key commercial role as a crossroad between China, the Middle East and Kievan Rus'. For some three centuries (c. 650–965) the Khazars dominated the vast area extending from the Volga-Don steppes to the eastern Crimea and the northern Caucasus.
Khazaria long served as a buffer state between the Byzantine empire and both the nomads of the northern steppes and the Umayyad empire, after serving as Byzantium's proxy against the Sasanian Persian empire. The alliance was dropped around 900. Byzantium began to encourage the Alans to attack Khazaria and weaken its hold on Crimea and the Caucasus, while seeking to obtain an entente with the rising Rus' power to the north, which it aspired to convert to Christianity. Between 965 and 969, the Kievan Rus' ruler Sviatoslav I of Kiev conquered the capital Atil and destroyed the Khazar state.
Originally, the Khazars were pagan Tengrist worshippers. The populace of the Khazar Khaganate appears to have been multi-confessional—a mosaic of pagan, Tengrist, Jewish, Christian and Muslim worshippers. The ruling elite of the Khazars was said by Judah Halevi and Abraham ibn Daud to have converted to Rabbinic Judaism in the 8th century, but the scope of the conversion within the Khazar Khanate remains uncertain. Proposals of Khazar origins have been made regarding the Slavic Judaising Subbotniks, the Bukharan Jews, the Muslim Kumyks, Kazakhs, the Cossacks of the Don region, the Turkic-speaking Krymchaks and their Crimean neighbours the Karaites to the Moldavian Csángós, the Mountain Jews and others.
In the late 19th century, a theory emerged that the core of today's Ashkenazi Jewry are genetically descended from a hypothetical Khazarian Jewish diaspora who had migrated westward from modern Russia and Ukraine into modern France and Germany. This theory still finds occasional support, but most scholars view it with skepticism. The theory is sometimes associated with antisemitism and anti-Zionism.