Nuclear warfare
After World War II, nuclear weapons were also developed by the Soviet Union (1949), the United Kingdom (1952), France (1960), and the People's Republic of China (1964), which contributed to the state of conflict and extreme tension that became known as the Cold War. In 1974, India, and in 1998, Pakistan, two countries that were openly hostile toward each other, developed nuclear weapons. Israel (1960s) and North Korea (2006) are also thought to have developed stocks of nuclear weapons, though it is not known how many. The Israeli government has never admitted or denied to having nuclear weapons, although it is known to have constructed the reactor and reprocessing plant necessary for building nuclear weapons. South Africa also manufactured several complete nuclear weapons in the 1980s, but subsequently became the first country to voluntarily destroy their domestically made weapons stocks and abandon further production (1990s). Nuclear weapons have been detonated on over 2,000 occasions for testing purposes and demonstrations.
High-alert nuclear weapon
Virtually all "high-alert nuclear weapons" are possessed by the U.S. and Russia. Both nations use automated command and control systems in conjunction with their early warning radar and/or satellites to facilitate the rapid launch of their land-based intercontinental ballistic missiles (ICBMs) and some submarine-launched ballistic missiles (SLBMs). Fear of a "disarming" nuclear first-strike that would destroy their command and control systems and nuclear forces led both nations to develop "launch-on-warning" capability, which requires high-alert nuclear weapons able to launch on a 30-minute (or less) tactical warning, the nominal flight time of ICBMs traveling between the U.S. and Russia.