No first use

No first use (NFU) refers to a pledge or a policy by a nuclear power not to use nuclear weapons as a means of warfare unless first attacked by an adversary using nuclear weapons. Earlier, the concept had also been applied to chemical and biological warfare.

China declared its NFU policy in 1964, and has since maintained this policy. India articulated its policy of no first use of nuclear weapons in 2003.

NATO has repeatedly rejected calls for adopting NFU policy, arguing that pre-emptive nuclear strike is a key option, in order to have a credible deterrent that could compensate for the overwhelming conventional weapon superiority enjoyed by the Soviet Army in the Eurasian land mass. In 1993, Russia dropped a pledge against first use of nuclear weapons made in 1982 by Leonid Brezhnev. In 2000, a Russian military doctrine stated that Russia reserves the right to use nuclear weapons "in response to a large-scale conventional aggression". This is because the balance of forces was reversed — NATO is now enjoying a clear superiority in conventional weapons.

China became the first nation to propose and pledge NFU policy when it first gained nuclear capabilities in 1964, stating "not to be the first to use nuclear weapons at any time or under any circumstances". During the Cold War, China decided to keep the size of its nuclear arsenal small rather than compete in an international arms race with the United States and the Soviet Union. China has repeatedly re-affirmed its no-first-use policy in recent years, doing so in 2005, 2008, 2009 and again in 2011. China has also consistently called on the United States to adopt a no-first-use policy, to reach a NFU agreement bilaterally with China, and to conclude an NFU agreement among the five nuclear weapon states. The United States has repeatedly refused these calls.

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Wikipedia