Almost every country has signed a treaty not to build nuclear weapons

The Nuclear Non-Proliferation Treaty opened for signature in 1968 and came into force in 1970. Countries without nuclear weapons promised not to acquire them; the five recognised nuclear states promised to work towards disarmament and share peaceful nuclear technology. It now has 191 parties, but India, Pakistan and Israel never joined, and North Korea announced its withdrawal in 2003.

— United Nations Office for Disarmament Affairs, Treaty on the Non-Proliferation of Nuclear Weapons — 1968