[Image:Nuclear weapon programs worldwide oct2006.png|thumb|300px|World map with nuclear weapons development status represented by color. ]] Nuclear proliferation is the spread of nuclear weapons, fissionable material, and weapons-applicable nuclear technology and information to nations not recognized as "Nuclear Weapon States" by the Treaty on the Nonproliferation of Nuclear Weapons, also known as the Nuclear Nonproliferation Treaty or NPT. Leading experts on nuclear proliferation, such as Etel Solingen of the University of California, Irvine, suggest that states' decisions to build nuclear weapons is largely determined by the interests of their governing domestic coalitions.