NATO is a political and military alliance between 26 North American and European countries formed in 1949. It was originally formed as a response to the threat of Soviet aggression and aimed to establish collective security. NATO is headquartered in Brussels and led by the Secretary General and Chairman of the Military Committee. Key functions include collective defense if a member country is attacked and stabilization of security conditions through economic and political cooperation. NATO has been involved in military operations in Bosnia, Kosovo, Afghanistan and elsewhere.