Nuclear umbrella

A “nuclear umbrella” is a guarantee by a nuclear-weapon state to defend a non-nuclear allied state. The context is usually the security alliances of the United States with Australia, Japan, South Korea, the North Atlantic Treaty Organization and the Compact of Free Association. Those alliances were formed because of the Cold War and the Soviet Union. For some countries, it was an alternative to acquiring nuclear weapons themselves; other alternatives include regional nuclear-weapon-free zones or nuclear sharing. Nuclear umbrellas are also referred to as “extended deterrence” under which a nuclear-weapon state extends its nuclear deterrent to cover threats against its non-nuclear-weapon state allies.