For the History.com, I wrote the ‘Nuclear Club’ and how nations join:
On October 6, 2006, North Korea announced it had detonated a nuclear bomb—making it the ninth nation to admit doing so. It wasn’t supposed to be that way. Until 2003, that country had been like all but a handful of countries, bound by the 1968 U.N. Non-Proliferation Treaty (NPT). That treaty allows peaceful nuclear technologies, but limits nuclear weapons to five nations: the United States, the Soviet Union (now Russia), the United Kingdom, France and the People’s Republic of China.
At its most stringent definition, the so-called ‘Nuclear Club’ has been limited to those five. Since 1971, they have also been the only members of the U.N. Security Council to hold permanent seats and veto power. Of the countries that never joined the NPT, four countries are believed to also have nuclear weapons. India and Pakistan have publicly acknowledged testing their own nuclear weapons, and Israel is widely assumed to have a significant arsenal. Along with North Korea, their programs are a testament to both the successes and failures of efforts to curb nuclear proliferation.