The International Security Assistance Force (ISAF) was a NATO-led security mission in Afghanistan established by the United Nations Security Council in December 2001 by Resolution 1386. Its main purpose was to train the Afghan national security forces and assist Afghanistan in rebuilding key government institutions, but also engaged in the Afghanistan War with the Taliban insurgency. From 2006 to 2011, the ISAF became increasingly involved in more intensive combat operations in southern and eastern Afghanistan. Troop contributors included the United States, the United Kingdom, and other NATO members, and a number of other countries. In December 2014, the ISAF ceased combat operations and was disbanded, with the USA withdrawing the vast majority of its troops from the country. Some troops remained behind in an advisory role as part of ISAF's successor, the Resolute Support Mission.