Islam in Central Asia has existed since the beginning of Islamic history. Sunni Islam is the most widely practiced religion in Central Asia. Shiism of Imami and Ismaili denominations predominating in the Pamir plateau and the western Tian Shan mountains (almost exclusively Ismailis), while boasting to a large minority population in the Zarafshan river valley, from Samarkand to Bukhara (almost exclusively Imamis). Islam came to Central Asia in the early part of the 8th century as part of the Muslim conquest of the region. Many well-known Islamic scientists and philosophers came from Central Asia, and several major Muslim empires, including the Timurid Empire and the Mughal Empire, originated in Central Asia. In the 20th century, severe restrictions on religious practice were enacted by the Soviet Union in Soviet Central Asia and the People's Republic of China in Xinjiang. Concerns about Islamic radicalism and religious freedom in the region persist to this day.