The Nuclear Nonproliferation Treaty (NPT), in force since 1970, is the cornerstone of global nuclear arms control. It divides the world into nuclear-weapon states (the U.S., Russia, China, the UK, and France) and non-nuclear-weapon states. Non-nuclear states agree not to acquire nuclear weapons; nuclear states agree to pursue disarmament. The International Atomic Energy Agency (IAEA) monitors compliance through inspections. Iran signed the NPT but has been the subject of IAEA findings of undeclared nuclear activities since 2002. Countries outside the NPT, including Israel and India, have developed nuclear weapons without legal prohibition.