On 4 April 1949, twelve nations signed the North Atlantic Treaty in Washington, D.C., establishing the North Atlantic Treaty Organization (NATO) as a collective defence alliance.
Formed in response to rising tensions with the Soviet Union, the treaty committed members to mutual defence, stating that an attack against one would be considered an attack against all.
NATO became a cornerstone of Western security during the Cold War and continues to play a central role in international military and political affairs.
