The Indus Valley civilization, one of the oldest in the world, dates back at least 5,000 years. Aryan tribes from the northwest infiltrated onto Indian lands about 1500 B.C.; their merger with the earlier Dravidian inhabitants created the classical Indian culture. Arab incursions starting in the 8th century and Turkish in the 12th were followed by those of European traders, beginning in the late 15th century. By the 19th century, Britain had assumed political control of virtually all Indian lands. Indian armed forces in the British army played a vital role in both World Wars. Nonviolent resistance to British colonialism led by Mohandas GANDHI and Jawaharlal NEHRU brought 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. Despite impressive gains in economic investment and output, India faces pressing problems such as the ongoing dispute with Pakistan over Kashmir, significant overpopulation, environmental degradation, extensive poverty, and ethnic and religious strife.