In 1963, U.S. intelligence projections forecast as many as 20 to 25 nuclear powers by the year 2000. The actual number today is nine: the United States, Russia, the United Kingdom, France, China, India, Pakistan, Israel, and North Korea. The first five are recognized as nuclear-weapon states under the NPT (defined as states that tested a device before January 1, 1967); the latter four developed or are believed to have developed weapons outside the treaty. The total global inventory is approximately 12,500 warheads, of which the U.S. and Russia possess roughly 5,000 each.
For the full account, see nuclear proliferation beyond the superpowers.
The NPT defines a “nuclear-weapon state” as a state that manufactured and exploded a nuclear weapon or other nuclear explosive device before January 1, 1967. The five that meet this definition are the United States (1945), the Soviet Union (1949, succeeded by Russia), the United Kingdom (1952), France (1960), and China (1964). The U.S. and Russia account for the great majority of the global stockpile. After START I and the bilateral reductions that followed, both countries have reduced deployed strategic warheads to roughly 1,500 each, though total inventories remain close to 5,000.
Of the four states outside the NPT: India has never signed, tested a “peaceful nuclear explosion” in 1974, and demonstrated weapons in the Pokhran-II tests of May 1998; the Indian arsenal is estimated at 160 warheads. Pakistan has never signed, and demonstrated weapons in the Chagai-I and Chagai-II tests of May 1998; the Pakistani arsenal is estimated at 170 warheads. Israel has never signed and has maintained deliberate nuclear ambiguity since the late 1960s, with an estimated arsenal of 100 to 200 warheads. North Korea signed the NPT in 1985, announced its withdrawal in 2003, and has conducted six nuclear tests, the most recent on September 3, 2017, with an estimated yield of 250 kilotons.
The non-proliferation regime has been more successful at slowing horizontal proliferation (the spread to additional states) than at producing vertical reductions (the decrease in size of existing arsenals). The number of nuclear-armed states has grown from five in 1964 to nine in 2024 — much slower than was predicted in 1960s scenarios that foresaw 20 or 25 nuclear powers by the century’s end.