On 11 September 2001, terrorists used passenger planes as weapons of mass destruction in their attack against targets located in the United States. The next day, on 12 September, for the first time in the Alliance’s history, the Allies invoked Article 5 of the Washington Treaty (NATO’s collective defense clause), confirming that an attack on one ally is considered as an attack on all allies. The Alliance took appropriate measures to support the United States of America. Under Operation Active Endeavour, NATO deployed ships to the eastern Mediterranean to detect vessels suspected of terrorist activity. NATO’s mission in Afghanistan was the largest military operation outside the Euro-Atlantic space. In December 2001, after the defeat of the terrorist groups al-Qaeda and the Taliban from Afghanistan, the leaders of the Afghan opposition held a conference in Bonn (Germany) to discuss the process of reconstruction and future development of the country. It was decided to form a new state structure – the interim government of Afghanistan and to form the International Security Assistance Force (ISAF) to ensure security in the country.

In January 2002, the ISAF Commander and the Afghan Transitional Authority signed Military Technical Agreement setting forth ISAF objectives. ISAF command originally rotated among different nations every six months. However, in 2003, the command was turned over indefinitely to NATO. ISAF was a United Nations-mandated international force that brought together military personnel from 51 countries. The purpose of the mission was to assist the Afghan government in establishing a safe environment that would contribute to the country’s development. ISAF’s mandate was initially limited to providing security in and around Kabul. In October 2003, the UN extended ISAF’s mandate to cover the whole of Afghanistan.   To further strengthen the international security forces, NATO created Provincial Reconstruction Teams – PRT under the command of ISAF. These groups composed of civilian and military personnel operated in the provinces of Afghanistan and helped the country’s authorities strengthen their powers and enhance security in the regions of Afghanistan; protected the security of international and non-governmental organizations in the territory of the country; participated in the works of restoring schools, medical institutions and water systems; supported the implementation of civil and military projects.

The NATO mission in Afghanistan, which lasted for 13 years, officially ended on 28 December 2014. Afghanistan proved over time that it could conduct military operations with its own self-defence forces without the assistance of ISAF combat forces.

The NATO-led mission Resolute Support Mission (RSM) in Afghanistan was launched on 1 January 2015. Its aim was to strengthen the Afghan National Security Forces, so that Afghanistan itself could fully and effectively control the situation in its territory.

In April 2021, NATO decided to end the mission in Afghanistan. The 20-year mission in Afghanistan was the longest military operation in American history. With the aforesaid decision, the United States of America changed the existing tactics of fighting terrorism in the region, which means the end of active military operations on the ground. Instead, counterterrorism operations will be carried out through pinpoint airstrikes by U.S. military bases in the region.