Countries with nuclear weapons

Possession means that weapons are located in the soveign terriroty of a country, not necessarily that they possess the means to control them.

NPT refers to the Treaty on the Non-Proliferation of Nuclear Weapons

"Declared" means that the government of the country has acknowldged that they possess nuclear weapons. Undclared means that the government of the country denies their possession, but is widely believed to possess them.