Unilateral disarmament is a policy option, to renounce weapons without seeking equivalent concessions from one's actual or potential rivals. It was most commonly used in the twentieth century in the context of unilateral nuclear disarmament, a recurrent objective of peace movements in countries such as the United Kingdom.
Nations do not often choose to dismantle their entire military capability. Unilateral disarmament is usually sought in one technical competency, such as weapons of mass destruction. Non-violent political movements from that of Mahatma Gandhi[1] to the Campaign for Nuclear Disarmament have recommended unilateral disarmament as a step toward world peace.
Unilateral nuclear disarmament could also happen were a series of cascading failures to occur. For example loss of expertise, inability to finance, recapitalize and maintain the existing nuclear capability. Procrastination and neglect of existing nuclear weapon platforms and infrastructure to such an extent that a nation is unable to reconstitute its nuclear capability in time before portions of the system(s) begin to break down. Where that nation's nuclear deterrence then becomes questionable and uncertain. [2]