The International Security Assistance Force (ISAF) was a multinational military mission in Afghanistan from 2001 to 2014. It was established by United Nations Security Council Resolution 1386 pursuant to the Bonn Agreement, which outlined the establishment of a permanent Afghan government following the U.S. invasion in October 2001. ISAF's primary goal was to train the Afghan National Security Forces (ANSF) and assist Afghanistan in rebuilding key government institutions; it gradually took part in the broader war in Afghanistan against the Taliban insurgency.

ISAF's initial mandate was to secure the Afghan capital of Kabul and its surrounding area against opposition forces to facilitate the formation of the Afghan Transitional Administration headed by Hamid Karzai. In 2003, NATO took command of the mission at the request of the UN and Afghan government, marking its first deployment outside Europe and North America. Shortly thereafter, the UN Security Council expanded ISAF's mission to provide and maintain security beyond the capital region. ISAF incrementally broadened its operations in four stages, and by 2006 took responsibility for the entire country; ISAF subsequently engaged in more intensive combat in southern and eastern Afghanistan.At its peak between 2010 and 2012, ISAF had 400 military bases throughout Afghanistan (compared to 300 for the ANSF) and roughly 130,000 troops. A total of 42 countries contributed troops to ISAF, including all 30 members of NATO. Personnel contributions varied greatly throughout the course of the mission: Initially, Canada was the largest contributor, though by 2010 the United States accounted for the majority of troops, followed by the United Kingdom, Turkey, Germany, France, and Italy; nations such as Georgia, Denmark, Norway, and Estonia were among the largest contributors per capita. The intensity of the combat faced by participating countries varied greatly, with the U.S. sustaining the most casualties overall, while British, Danish, Estonian, and Georgian forces suffered the most deaths for their size.

Pursuant to its ultimate aim of transitioning security responsibilities to Afghan forces, ISAF ceased combat operations and was disbanded in December 2014. A number of troops remained to serve a supporting and advisory role as part of its successor organization, the Resolute Support Mission.

The North Atlantic Treaty Organization (NATO, ; French: Organisation du traité de l'Atlantique nord, OTAN), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states, 28 of which are in Europe and the other 2 being part of North America. Established in the aftermath of World War II, the organization implements the North Atlantic Treaty, signed 4 April 1949.NATO constitutes a system of collective security, whereby its independent member states agree to mutual defense in response to an attack by any external party. It was established during the Cold War in response to the threat posed by the Soviet Union. The alliance has remained in place since the end of the Cold War, and has been involved in military operations in the Balkans, the Middle East, South Asia, and Africa. The NATO headquarters is located in Brussels, Belgium, while the headquarters of Allied Command Operations is near Mons, Belgium. The organization's motto is "animus in consulendo liber" (Latin for "A mind unfettered in deliberation").Since its founding, the admission of new member states has increased the alliance from the original 12 countries to 30. The most recent member state to be added to NATO was North Macedonia on 27 March 2020. NATO currently recognizes Bosnia and Herzegovina, Georgia, and Ukraine as aspiring members. Enlargement has led to tensions with non-member Russia, with Russian president Vladimir Putin demanding that NATO provide legal guarantees that it would stop expanding east (to countries such as Ukraine, Georgia or Moldova).

An additional 20 countries participate in NATO's Partnership for Peace programme, with 15 other countries involved in institutionalized dialogue programmes. The combined military spending of all NATO members in 2020 constituted over 57 per cent of the global nominal total. Members agreed that their aim is to reach or maintain the target defence spending of at least 2 per cent of their GDP by 2024.