The territory of Kazakhstan has historically been inhabited by nomadic groups and empires. In antiquity, the nomadic Scythians inhabited the land and the Persian Achaemenid Empire expanded towards the southern territory of the modern country. Turkic nomads, who trace their ancestry to many Turkic states such as the First and Second Turkic Khaganates, have inhabited the country throughout its history. In the 13th century, the territory was subjugated by the Mongol Empire under Genghis Khan. By the 16th century, the Kazakh emerged as a distinct group, divided into three "jüz". The Russians began advancing into the Kazakh steppe in the 18th century, and by the mid-19th century, they nominally ruled all of Kazakhstan as part of the Russian Empire. Following the 1917 Russian Revolution, and subsequent civil war, the territory of Kazakhstan was reorganised several times. In 1936, it was made the Kazakh Soviet Socialist Republic, part of the Soviet Union. Kazakhstan was the last of the Soviet republics to declare independence during the dissolution of the Soviet Union in 1991. Human rights organisations have described the Kazakh government as authoritarian, and regularly describe Kazakhstan's human rights situation as poor.