There is much uncertainty as to the time when the concept of yasak was introduced in Muscovy. It appears likely that the tax was inherited by Muscovy from the Volga khanates of Kazan and Astrakhan - two fragments of the Golden Horde that were subjugated by Ivan IV in the 1550s. These territories were settled by a range of non-Christian peoples who were expected to pay yasak either in kind or cash. The late French scholar of Eurasian history, Renee Grousset, traces "yasaq" (Regulations) back still further in his classic work, "The Empire of the Steppes", to the moral code imposed by Genghis Khan on his original horde. The Yasaq continued to be practiced by Mongol hordes until they came under Yellow Church Buddhist (Mongolia, China) and Muslim influences (Golden Horde, Persia, Central Asia) in successive centuries.