At the dawn of the nuclear age, the United States hoped to maintain a monopoly on its new weapon, but the secrets and the technology for making nuclear weapons soon spread. Four years after the United States conducted its first nuclear test explosion in July 1945 and dropped atomic bombs on the cities of Hiroshima and Nagasaki in August 1945, the Soviet Union conducted its first nuclear text explosion. The United Kingdom (1952), France (1960), and China (1964) followed. Seeking to prevent the nuclear weapon ranks from expanding further, the United States and other like-minded states negotiated the nuclear Nonproliferation Treaty (NPT) in 1968 and the Comprehensive Nuclear Test Ban Treaty (CTBT) in 1996.

Since the inception of the NPT, several states have abandoned nuclear weapons programs, but others have defied the NPT. India, Israel, and Pakistan have never signed the treaty and possess nuclear arsenals. Iraq initiated a secret nuclear program under Saddam Hussein before the 1991 Persian Gulf War. North Korea announced its withdrawal from the NPT in January 2003 and has tested nuclear devices since that time. Iran and Libya have pursued secret nuclear activities in violation of the treaty’s terms, and Syria is suspected of doing the same. Still, nuclear nonproliferation successes outnumber failures and dire forecasts decades ago that the world would be home to dozens of states armed with nuclear weapons have not come to pass.

At the time the the NPT was concluded, the nuclear stockpiles of the the United States and the Soviet Union/Russia numbered in the tens of thousands. Beginning in the 1970s, U.S. and Soviet/Russian leaders negotiated a series of bilateral arms control agreements and initiatives that limited, and later, reduced the size of their nuclear arsenals. Despite that progress, the United States and Russia still deploy more than 1,500 strategic warheads on several hundred bombers and missiles—far more than necessary to deter nuclear attack—and they are modernizing their nuclear delivery systems. If these weapons were used even in a “limited” way, the result would be catastrophic nuclear devastation.

Today, other nuclear arms states, China, India, and Pakistan, in particular, are all pursuing new ballistic missile, cruise missile, and sea-based nuclear delivery systems. In addition, Pakistan has dangerously lowered the threshold for nuclear weapons use by developing tactical nuclear weapons capabilities to counter perceived Indian conventional military threats. North Korea continues its nuclear pursuits in violation of its earlier denuclearization pledges. These arsenals, although smaller in number, are dangerous and destabilizing.

Read more: https://www.armscontrol.org/factsheets/Nuclearweaponswhohaswhat