Judaism being a notable (if historically contested) episode in the religion's history. The Alans were a major Muslim people group, who faced the invading Mongols and their Tengrist practices, with some of the latter settling permanently. The later Nogais were Muslim, but were replaced by the contemporaneous Kalmyks, who practice Buddhism. With the annexation of the region by the Russian Empire, there was an influx of Slavic-speaking Christian settlers. Many religious institutions were suppressed in the wake of the Russian Revolution. Kalmyk autonomy The ancestors of the Kalmyks, the Oirats, migrated from the steppes of southern Siberia on the banks of the Irtysh River, reaching the Lower Volga region by the early 17th century. Historians have given various explanations for the move, but generally recognise that the Kalmyks sought abundant pastures for their herds. Another motivation may have involved escaping the growing dominance of the neighbouring Dzungar Mongol tribe. They reached the lower Volga region in or about 1630. That land, however, was not uncontested pastures, but rather the homeland of the Nogai Horde, a confederation of Turkic-speaking nomadic tribes. The Kalmyks expelled the Nogais, who fled to the Caucasian plains and to the Crimean Khanate, areas (at least theoretically) under the control of the Ottoman Empire. Some Nogai groups sought the protection of the Russian garrison at Astrakhan. The remaining nomadic Mongol Oirat tribes became vassals of the Kalmyk Khan. The Kalmyks settled in the wide-open steppes – from Saratov in the north to Astrakhan on the Volga delta in the south and to the Terek River in the southwest. They also encamped on both sides of the Volga River, from the Don River in the west to the Ural River in the east. Although these territories had been recently annexed by the Tsardom of Russia, Moscow was in no position to settle the area with Russian colonists. This area under Kalmyk control would eventually be called the Kalmyk Khanate. Within twenty-five years of settling in the Lower Volga region, the Kalmyks became subjects of the Tsar of Russia. In exchange for protecting Russia's southern border, the Kalmyks were promised an annual allowance and access to the markets of Russian border settlements. The open access to Russian markets was supposed to discourage mutual raiding on the part of the Kalmyks and of the Russians and Bashkirs, a Russian-dominated Turkic people, but this was not often the practice. In addition,