Proposed U.S. strategic defense system against nuclear attacks. Announced as a 20-year, $20 billion effort by Pres. Ronald Reagan in 1983, SDI was intended to defend the U.S. from a full-fledged Soviet attack by intercepting ICBMs in flight. The interception was to be effected by technology not yet developed, including space- and ground-based laser stations and air- and ground-based missiles. The space component of SDI led to its being derisively dubbed “Star Wars” after the popular film. Though the program was roundly criticized by opposition politicians and arms-control advocates as unworkable and as a dangerous violation of the Antiballistic Missile (ABM) Treaty of 1972, Congress granted initial funding for it. Early development efforts were largely unsuccessful, and with the fall of the Soviet Union in 1991 the concept lost urgency. During the Bush and Clinton administrations, ballistic missile defense was scaled back to focus on protecting the U.S. from limited attack by a “rogue” state or a single accidentally launched missile. In 2002 the U.S. withdrew from the ABM treaty to begin active testing of a limited antimissile program. Seealso antiballistic missile.
Learn more about Strategic Defense Initiative (SDI) with a free trial on Britannica.com.
Negotiations between the U.S. and the Soviet Union aimed at curtailing the manufacture of strategic nuclear missiles. The first round of negotiations began in 1969 and resulted in a treaty regulating antiballistic missiles and freezing the number of intercontinental ballistic missiles and submarine-launched ballistic missiles. It was signed by Leonid Brezhnev and Richard Nixon in 1972. A second round of talks (1972–79), known as SALT II, addressed the asymmetry between the two sides' strategic forces and ended with an agreement to limit strategic launchers (see MIRV). Signed by Brezhnev and Jimmy Carter, it was never formally ratified by the U.S. Senate, though its terms were observed by both sides. Subsequent negotiations took the name Strategic Arms Reduction Talks (START). Seealso intermediate-range nuclear weapons; Nuclear Test-Ban Treaty.
Learn more about Strategic Arms Limitation Talks (SALT) with a free trial on Britannica.com.