Nuclear weapon

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either nuclear fission (fission or atomic bomb) or a combination of fission and nuclear fusion reactions (thermonuclear weapon), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter. Nuclear warfare is widely considered a global catastrophic risk. Nine sovereign states are known or believed to possess nuclear weapons as of 2026: the United States, Russia, the United Kingdom, France, China, India, Pakistan, North Korea and Israel.

The majority of nuclear weapons have energy yields between 100 and 1,000 kilotons of TNT. Yields in the low kilotons can destroy cities. The effects of nuclear weapons include extreme blast damage, heat, ionizing radiation, and firestorms, followed by radioactive nuclear fallout, an electromagnetic pulse, radar blackout, and acute or chronic radiation syndrome in humans and animals. Hundreds of nuclear explosions would likely cause nuclear winter and nuclear famine.

The first nuclear weapons were developed by the United States in collaboration with the United Kingdom and Canada during World War II in the Manhattan Project. Production requires a large scientific-industrial complex, primarily for fissile material, either nuclear reactors and reprocessing plants producing plutonium, or uranium enrichment facilities. Nuclear weapons have been used twice in war, in the 1945 atomic bombings of Hiroshima and Nagasaki that killed between 150,000 and 246,000 people.