The large deserts, semi-deserts and steppes of Kazakhstan are located to the south of the Ural mountain ridge and the west Siberian lowland, with the Russian Volga basin and the Caspian Sea in the west, the Altai mountains in the east and the Aral Lake and Uzbekistan in the south. The country has historically been inhabited by nomadic tribes of Mongol and Turkish origin and since the nineteenth century (when Russian administration was enforced) also by Russians and Ukrainians. In Soviet history, several ethnic groups were deported to Kazakhstan, many of which left after 1991 (the largest being Russians and Germans), while Kazakhs abroad returned. Today, Russians are concentrated in the north and the Kazakhs in the south. The population amounts to some 15 million. Islam was introduced among the nomads only in the eighteenth and nineteenth centuries and the country is fairly secularized. In 1924, a KazakhKyrgyz Autonomous Republic within Russia was created and in 1936 Kazakhstan became a Soviet Republic.