The Indus Valley civilization, one of the oldest in the world, goes back at least 5,000 years. Aryan tribes from the northwest invaded about 1500 B.C.; their merger with the earlier inhabitants created the classical Indian culture. Arab incursions starting in the 8th century and Turkish in 12th were followed by European traders, beginning in the late 15th century. By the 19th century, Britain had assumed political control of virtually all Indian lands. Nonviolent resistance to British colonialism under Mohandas GANDHI and Jawaharlal NEHRU led to independence in 1947. The subcontinent was divided into the secular state of India and the smaller Muslim state of Pakistan. A third war between the two countries in 1971 resulted in East Pakistan becoming the separate nation of Bangladesh. Fundamental concerns in India include the ongoing dispute with Pakistan over Kashmir, massive overpopulation, environmental degradation, extensive poverty, and ethnic and religious strife, all this despite impressive gains in economic investment and output.