The 9/11 terrorist attacks prompted the United States to invoke NATO’s Article 5 collective security clause, signaling that an attack against one member was an attack against all. The United Kingdom, as a founding member of the alliance, responded by committing forces to Afghanistan alongside the United States. This decision was based on the alliance’s binding security provisions and the broader objective of preventing further terrorist activity worldwide.

_2_ The UK’s engagement in Afghanistan began in 2001 and continued in various phases over more than two decades. It was a component of the International Security Assistance Force (ISAF) established under NATO auspices, which coordinated multinational military and reconstruction efforts. British forces participated in combat operations, training Afghan security forces, and supporting stabilization projects. Their presence transitioned from a predominantly combat role to a focus on mentoring and capacity building as the security environment evolved.

_3_ The extended UK deployment illustrates the practical application of NATO’s collective security principles beyond the immediate United States‑led response. It also underscored the UK’s commitment to multilateral cooperation in addressing global security challenges. The experience contributed to refining NATO’s operational doctrines, enhancing interoperability among member states, and shaping the UK’s subsequent defence and foreign‑policy priorities within the broader context of international alliance structures.