Nuclear weapons are weapons of mass destruction that derive their destructive force from nuclear reactions, the fission or fusion of the atom.
To make a nuclear weapon, either highly enriched uranium (containing more than 90 per cent of uranium) from uranium enrichment plants or plutonium separated in reprocessing plants from spent fuel rods is needed. Depending on the size and location of the explosion (on the ground or in the air), one single nuclear bomb can destroy large areas and kill many tens of thousands, even hundreds of thousands of people.
Towards the end of World War II; after the surrender of Adolf Hitler, when war was still going on in Asia against Japan, the United States dropped one atomic bomb on Hiroshima (6 August 1945) and one on Nagasaki (9 August of the same year).
So-called radiological dispersal devices ("dirty bombs") that scatter radiological material when they are detonated with conventional explosives do not fall under the category of nuclear weapons as they do not trigger a nuclear chain reaction.