Nuclear weapons are powerful devices that use nuclear reactions to cause massive destruction. The official nuclear powers recognized under the Non-Proliferation Treaty (NPT) are the United States, Russia, China, France, and the United Kingdom. These nations are also permanent members of the UN Security Council. Non-NPT nuclear-armed states include India, Pakistan, and North Korea, while Israel is believed to have nuclear weapons, though undeclared. These weapons are a major global security concern, prompting efforts for arms control and non-proliferation.