There are some treaties about the nuclear weapons

Concerns about the terrifying consequences of such weapons have led governments to negotiate arms control agreements like the Nuclear Test-Ban Treaty of 1963 and the Treaty on the Non-proliferation of Nuclear Weapons of 1968, even as many nations have developed nuclear weapons of much greater strength than those used against the Japanese cities. Because of their sheer destructive potential, these weapons have given rise to a new branch of military strategy and planning known as nuclear strategy, which has its internal logic and set of doctrines.

Five governments are recognized as nuclear-weapon states by the Treaty on the Non-Proliferation of Nuclear Weapons of 1970 (commonly known as the Non-Proliferation Treaty or NPT): the United States, Russia, the United Kingdom, France, and China (these are also, not coincidently, the five permanent members of the United Nations Security Council). Nuclear devices have also been tested by India and Pakistan. Israel is thought to possess nuclear weapons, however, they have never been acknowledged or tested. It is thought that North Korea has nuclear weapons but no rockets to deliver them.