The authors calculate that some 125,000 nuclear warheads have been built since 1945, about 97 percent of them by the United States and the Soviet Union and Russia. The nine nations with nuclear weapons now possess more than 10,000 nuclear warheads in their military stockpiles, the authors estimate, with several thousand additional US and Russian retired warheads in storage, awaiting dismantlement. The nuclear stockpiles of China, as well as Pakistan, India, Israel, and North Korea, are minuscule in comparison with the US and Russian arsenals, but more difficult to estimate. Still, the authors believe that China’s nuclear weapons stockpile has surpassed Great Britain’s. Although the total number of nuclear warheads in the world is decreasing because of US and Russian reductions, all the nations with nuclear weapons continue to modernize or upgrade their nuclear arsenals.