North Atlantic Treaty (NATO)

4 April 1949 · Washington, D.C.

Cold War & arms control

Background

Formed to deter Soviet expansion after the Second World War. Founding members included the USA, UK, France and Canada; NATO has since grown to 32 members, with Finland (2023) and Sweden (2024) the newest. Its headquarters is in Brussels.

Signed by

USA, Canada and ten Western European countries

Why it matters

Created NATO. Article 5 says an armed attack on one member is an attack on all; it has been used only once, after the 11 September 2001 attacks.