Part of the Indian Mogul empire, Afghanistan became independent in the mid 18th century, and in the 19th and early 20th centuries was a focal point for conflicting Russian and British interests on the North-West Frontier. Afghanistan was invaded by the Soviet Union in 1979; after Soviet forces withdrew in 1988-9 the country was thrown into turmoil with various Islamic groups struggling for power. In 1996 the Taliban gained control of Kabul and set up an Islamic state: this was overthrown in 2001 by US-led forces in conjunction with Afghan groups following the attacks on the World Trade Center and the Pentagon on 11 September 2001. A new government was formed, but instability continued in many areas of the country