The United Nations (UN) is an intergovernmental organization to promote international co-operation. A replacement for the ineffective League of Nations, the organization was established on 24 October 1945 after World War II in order to prevent another such conflict. At its founding, the UN had 51 member states; there are now 193. The headquarters of the United Nations is inManhattan, New York City, and experiences extraterritoriality. Further main offices are situated in Geneva, Nairobi, and Vienna. The organization is financed by assessed and voluntary contributions from its member states. Its objectives include maintaining international peace and security, promoting human rights, fostering social and economic development, protecting the environment, and providing humanitarian aid in cases of famine, natural disaster, and armed conflict.
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion (thermonuclear weapon). Both reactions release vast quantities of energy from relatively small amounts of matter. The first test of a fission (“atomic”) bomb released the same amount of energy as approximately 20,000 tons of TNT (84 TJ). The first thermonuclear (“hydrogen”) bomb test released the same amount of energy as approximately 10 million tons of TNT (42 PJ).