Among the most important treaties signed in the postwar years by the United States, despite their inadequacies, were those seeking to ban nuclear testing and to limit the proliferation of nuclear arms. It also became apparent in the years following World War II that national security would extend to activities in outer space. At first, in the face of obvious Soviet satellite superiority, the United States was determined to act unilaterally to assure its security from attack. But NATO had created a situation whereby Europe was dependent upon U.S. nuclear protection, and these obligations placed restraints upon the U.S. capacity to act unilaterally in relation to nuclear defense. Public opposition at home and in Europe to the threat of nuclear destruction forced the United States and the Soviet Union to stabilize the balance of their nuclear strategic weapon systems through some form of treaty arrangement. The first such treaty, the Treaty of Moscow, known as the Limited Nuclear Test-Ban Treaty (the United States, the Soviet Union, the United Kingdom), banning nuclear tests in space, in the atmosphere, and underwater, was signed on 5 August 1963. It was approved on 24 September by the Senate, 80 to 19. As of 2001, more than 100 nations had signed it.
A treaty regarding the nonproliferation of nuclear arms was signed on 1 July 1968. It had been presented to the Geneva disarmament conference on 11 March by the United States and the Soviet Union. A resolution recommending the signing of the treaty was voted on 12 June 1968 by the General Assembly of the United Nations, 95 to 4, with 21 abstentions. As with the Test Ban Treaty, France and China refused to endorse it.
In June 1968 the United States and the Soviet Union began disarmament negotiations aimed at restricting the construction of launching devices for nuclear and thermonuclear projectiles. Such was to be the objective of the Strategic Arms Limitation Talks (SALT). On the occasion of President Richard M. Nixon's trip to the Soviet Union (22–30 May 1972), many economic and technical accords were signed. Among the most important was an Anti-Ballistic Missile (ABM) Treaty limiting the number of missiles and launchers each side could deploy. The Senate approved the ABM treaty by a vote of 88 to 2. A further major accord concerning the prevention of nuclear war was signed on 22 June during Leonid Brezhnev's visit to Washington, D.C. (16–25 June 1973). A number of agreements curbing nuclear testing were signed (3 July 1974) during Nixon's Moscow visit to meet with Brezhnev for the third time.
SALT bogged own, but negotiations on European cooperation and security came to fruition. In July 1975, President Gerald Ford traveled to Helsinki to attend a summit meeting of thirty-five nations and signed an accord that recognized Europe's boundaries as inviolable and provided vaguely for improvement of human rights, such as emigration and access to information, even in communist bloc countries. President Jimmy Carter made clear subsequently that arms control and the issue of the human rights element in the Helsinki Accords was at the core of relations with the Soviet Union. When Secretary of State Cyrus R. Vance visited Moscow late in March 1977 hoping to conclude a SALT II agreement, the Soviets flatly rejected his proposals, indicating that Washington's rhetoric on human rights displeased them as meddling in their internal affairs. However, a new SALT II agreement was reached in 1979 placing a ceiling on intercontinental ballistic missiles (ICBMs). Although not ratified, the United States and the Soviet Union more or less honored its terms.
In 1983 Republican President Ronald Reagan announced the Strategic Defense Initiative (SDI), a space-based defense system against nuclear attack. SDI would not only have destabilized the nuclear balance with the Soviet Union, it would certainly have violated the spirit if not the letter of the 1972 ABM treaty. In 1985 Reagan initiated the Strategic Arms Reduction Talks (START) with Soviet leader Mikhail Gorbachev, but no treaty resulted in the ensuing summit meetings because of Reagan's adherence to the highly controversial SDI. Of special concern were intermediate-range land-based cruise and ballistic missiles (range of 500 to 1,000 kilometers). Finally, Reagan and Gorbachev signed the Intermediate-Range Nuclear Forces (INF) Treaty in 1987, which aimed to reduce and eliminate rather than, as in previous arms agreements, limit a class of weapons. The Senate ratified the treaty, with conditions, on 27 May 1988, by a vote of 93 to 5. The treaty was to stay in effect until 2001. Reagan's successor, George H. W. Bush, signed a START agreement with Gorbachev in Moscow in 1991, and in 1993, after the breakup of the Soviet Union, he signed a START II treaty with Russian President Boris Yeltsin.
Following the adoption of a resolution calling for a comprehensive nuclear test ban treaty (CTBT) in the United Nations General Assembly in December 1993, negotiations on a CTBT began in the Conference on Disarmament in Geneva in January 1994. On 10 September 1996 the UN General Assembly approved the CTBT by an over-whelming vote of 158 to 3, with five nations abstaining. On 24 September 1996, President Bill Clinton became the first national leader to sign the treaty, and the White House submitted it to the U.S. Senate for ratification in September 1997. Despite overwhelming public support, after a long delay the Senate rejected it on 13 October 1999 by a vote of 51 to 48.
More than 160 nations had signed the CTBT by 2001, but of the original five nuclear powers (Britain, China, France, Russia, and United States), only Britain, France, and Russia had ratified it. The treaty required the ratification of forty-four specific countries, including the United States. These were nations that had nuclear power reactors or nuclear research facilities; all were members of the Conference on Disarmament. This group included India and Pakistan, both of which tested nuclear devices in May 1998. India and Pakistan (and China) were thought unlikely to ratify the treaty unless the United States did so first.
The Clinton administration supported a CTBT that would contain the usual clause permitting a state to withdraw from the treaty for reasons of "supreme national interest." (The maintenance of a safe and reliable nuclear stockpile was considered to be a supreme national interest of the United States.) President Bush declared a moratorium on the testing of nuclear weapons in 1992, and, by 2001, the United States had not conducted a nuclear test since that time. The disappearance of Cold War bipolarity brought an end to the strategic world it created and sharply reduced the sense of mutual vulnerability experienced by the two superpowers. The basic philosophy behind the 1972 ABM treaty, which banned the deployment of nationwide defenses against missile attacks, was that no nation would risk launching a missile attack if it was left defenseless against a retaliatory strike. After the Gulf War of 1991, however, the United States argued that the spread of missile technology required advanced nations to erect defenses against at least the handful of missiles that could one day be launched against them by terrorists or rogue states. This, of course, would mean that the ABM treaty would have to be adjusted to accommodate a new strategic reality.
President Clinton pushed for unilaterally constructing a partial missile defense system, which he claimed would protect the United States against the new threat. Russia objected, claiming that this would violate the ABM Treaty and start the major nuclear powers on a new, defensive dimension of the arms race. Yeltsin's successor, Russian President Vladimir V. Putin, argued that mutual reduction was the path to stability. There were good political reasons to cooperate with Russia, and in May 2001, President George W. Bush offered Russia a package to broaden the scope of missile defense technology to enlist Russian support for the new system.
By the early twenty-first century there was a broad consensus emerging in the United States that it was in the American national security interest to develop a limited missile defense commensurate with the emergence of real threats and the technology available. The politics of missile defense internationally would require cooperation with allies and Russian involvement. In relation to China, the other major concern for American policymakers, missile defense would also have to be handled as a part of the overall U.S.–China relationship.
The move toward cautious cooperation with Russia at the end of the Cold War was also evident in the peaceful use and exploration of outer space. For thirty years after World War II, the United States had primarily regarded space as an area of competition. Tentative steps toward cooperation had been taken in the 1970s, symbolized by the 1975 Apollo-Soyuz docking. In 1988 the Reagan administration signed an agreement with ten European nations, Canada, and Japan to undertake technological collaboration in space and human space flights, but little came of the collaboration until Russia joined in 1993.