Specifically, the spread of nuclear weapons, and, more generally, the spread of nuclear technology and knowledge that might be put to military use. Most concern is given to horizontal proliferation: the spread of nuclear weapons to states not yet possessing them. Vertical proliferation—the increase in numbers or dispersion of nuclear weapons by nuclear weapons states—has become of less concern since the winding down of the superpower arms race, although slow disarmament is of concern to non‐nuclear states. Nuclear proliferation is controlled by the Nuclear Non‐proliferation Treaty (NPT), which recognizes five nuclear states. However, some states remain outside the treaty and have developed nuclear capabilities. Increasingly, the prospect of nuclear weapons in the hands of terrorist organizations, such as al‐Qaeda, is creating concern. Nuclear proliferation is widely considered to be a problem because of the fear that it will increase the probability of nuclear weapons being used. Some argue that nuclear proliferation could enhance international security by spreading the paralysing effects of deterrence in regions that otherwise have a high probability of recurrent conventional war. Because of the close links between civil and military nuclear technology, many states are able to reduce the time necessary to acquire a nuclear weapon by acquiring a range of nuclear technologies for civil purposes. Several states have already achieved threshold status, in which they either have unannounced nuclear weapon capabilities, or could develop them extremely quickly if necessary.
Subjects: Politics — Warfare and Defence.