A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or from a combination of fission and fusion reactions (thermonuclear bomb). Both bomb types release large quantities of energy from relatively small amounts of matter. Today, nine states have nuclear weapons and many more can easily acquire those, although only five states are officially recognized as possessing nuclear weapons by the 1968 nuclear Non Proliferation Treaty (NPT). Those are • The United States (1945) • Russia (1949) • The United Kingdom (1952) • France (1960) and • China (1964) Four states never joined the NPT but are known to possess nuclear weapons: • Israel • India (1974) • Pakistan (1998) and • North Korea (2006)