Tashtyk cultures of the Yenisey valley and Altay Mountains are associated with the Indo-European migrations across Eurasia. The proto-Mongol Khitan people also occupied parts of the region. In the 13th century, during the period of the Mongol Empire, the Mongols conquered a large part of this area. With the breakup of the Golden Horde, the autonomous Khanate of Sibir formed in the late-15th century. Turkic-speaking Yakut migrated north from the Lake Baikal region under pressure from the Mongol tribes during the 13th to 15th century. Siberia remained a sparsely populated area. Historian John F. Richards wrote: "... it is doubtful that the total early modern Siberian population exceeded 300,000 persons". The growing power of Russia in the West began to undermine the Siberian Khanate in the 16th century. First, groups of traders and Cossacks began to enter the area. The Russian Army was directed to establish forts farther and farther east to protect new Russian settlers who migrated from Europe. Towns such as Mangazeya, Tara, Yeniseysk, and Tobolsk developed, the last becoming the de facto capital of Siberia from 1590. At this time, Sibir was the name of a fortress at Qashliq, near Tobolsk. Gerardus Mercator, in a map published in 1595, marks Sibier both as the name of a settlement and of the surrounding territory along a left tributary of the Ob. Other sources contend that the Sibe, an indigenous Tungusic people, offered fierce resistance to Russian expansion beyond the Urals. Some suggest that the term "Siberia" is a russification of their ethnonym. Russian Empire By the mid-17th century, Russia had established areas of control that extended to the Pacific Ocean. Some 230,000 Russians had settled in Siberia by 1709. Siberia became one of the destinations for sending internal exiles. Exile was the main Russian punitive practice with more than 800,000 people exiled during the nineteenth century. The first great modern change in Siberia was the Trans-Siberian Railway, constructed during 1891–1916. It linked Siberia more closely to the rapidly industrialising Russia of Nicholas II (). Around seven million Russians moved to Siberia from Europe between 1801 and 1914. Between 1859 and 1917 more than half a million people migrated to the Russian Far East. Siberia has extensive natural resources: during the 20th century, large-scale exploitation of these took place, and industrial towns cropped up throughout the region. At 7:15 a.m. on 30 June 1908 the Tunguska Event felled millions