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.
Nuclear weapons of the United States
In 2009 and 2010, the administration of President Barack Obama declared policies that would invalidate the Bush-era policy for use of nuclear weapons and its motions to develop new ones. First, in a prominent 2009 speech, U.S. President Barack Obama outlined a goal of "a world without nuclear weapons". To that goal, U.S. President Barack Obama and Russian Prime Minister Dmitry Medvedev signed a new START treaty on April 8, 2010, to reduce the number of active nuclear weapons from 2,200 to 1,550. That same week Obama also revised U.S. policy on the use of nuclear weapons in a Nuclear Posture Review required of all presidents, declaring for the first time that the U.S. would not use nuclear weapons against nonnuclear, NPT-compliant states. The policy also renounces development of any new nuclear weapons.