European countries lack sufficient funds to independently finance their defense if the United States leaves NATO

Overview of major milestones in the evolving relationship between the United States and NATO.

The alliance's cooperation with Western partners: collective defence and deterrence, defence-industrial and technology investment, burden-sharing and the coordination of military support among member states and allied governments.

Security arrangement under which states commit to treat an attack on one as an attack on all, obliging joint response. Underpins alliances such as NATO and provisions of the UN Charter, making shared deterrence and coordinated military planning central instruments of international stability.