Proliferation is the spread of military capability and technology from one state or actor to others in a manner that produces instability and heightens the risk of conflict and increases military threats to neighboring states. The concept is most commonly referred to in the context of the spread of nuclear weapons capabilities and the increasing number of states with or desiring to acquire nuclear weapons.

However, proliferation can be applied to other types of military capability. Other weapons of mass destruction (WMDs), such as chemical or biological weapons, are commonly considered in the context of proliferation, as is advanced conventional military capabilities, such as long-range cruise and ballistic missile capabilities that can act as delivery vehicles for WMDs. The process by which proliferation is countered is ...