A nuclear weapon (also called an atom bomb, nuke, atomic bomb, nuclear warhead, A-bomb, or nuclear bomb) 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. Nuclear weapons have only been used twice, both times by the United States against Japan near the end of World War II.
Nukes are considered the most destructive weapons in the world – their explosions are so powerful, just one nuclear bomb could destroy an entire city. They’re far more damaging than even the biggest normal, non-nuclear bombs. They release huge amounts of radiation – which can cause radiation sickness – so their actual impact lasts longer than the blast. Nine countries currently have nuclear weapons: the US, UK, Russia, France, China, India, Pakistan, Israel and North Korea.