<P> Economic problems caused by the arms race in both powers, combined with China's new role and the ability to verify disarmament led to a number of arms control agreements beginning in the 1970s . This period known as détente allowed both states to reduce their spending on weapons systems . SALT I and SALT II limited the size of the states' arsenals . Bans on nuclear testing, anti-ballistic missile systems, and weapons in space all attempted to limit the expansion of the arms race through the Partial Test Ban Treaty . </P> <P> In 1958, both the U.S. and Soviet Union agreed to informally suspend nuclear testing . However, this agreement was ended when the Soviets resumed testing in 1961, followed by a series of nuclear tests conducted by the U.S. These events led to much political fallout, as well as the Cuban Missile Crisis in 1962 . Something had to be done to ease the great tensions between these two countries, so on October 10, 1963, the Limited Test Ban Treaty (LTBT) was signed . This was an agreement between the U.S., Soviet Union, and the U.K., which significantly restricted nuclear testing . All atmospheric, underwater, and outer space nuclear testing were agreed to be halted, but countries were still allowed to test underground . An additional 113 countries have signed this treaty since 1963 . </P> <P> In November, 1969, Strategic Arms Limitation Talks (SALT) begun . This was primarily due to the economic impact that nuclear testing and production had on both U.S. and Soviet economies . The SALT I Treaty, which was signed in May, 1972, produced an agreement on two significant documents . These were the Anti-Ballistic Missile Treaty (ABM Treaty) and the Interim Agreement on the Limitation of Strategic Offensive Arms . The ABM treaty limited each country to two ABM sites, while the Interim Agreement froze each country's number of intercontinental ballistic missiles (ICBMs) and submarine - launched ballistic missiles (SLBMs) at current levels for five years . This treaty significantly reduced nuclear - related costs as well as the risk of nuclear war . However, SALT I failed to address how many nuclear warheads could be placed on one missile . A new technology, known as multiple - independently targetable re-entry vehicle (MIRV), allowed single missiles to hold and launch multiple nuclear missiles at targets while in mid-air . Over the next 10 years, the Soviet Union and U.S added 12,000 nuclear warheads to their already built arsenals . </P> <P> Throughout the 1970s, both the Soviet Union and United States replaced old missiles and warheads with newer, more powerful and effective ones . This continued to worsen Soviet - U.S relations . On June 18, 1979, the SALT II treaty was signed in Vienna . This treaty limited both sides' nuclear arsenals and technology . However, this treaty as well as the era of the détente ended with the Soviet Union's invasion of Afghanistan in January, 1980 . The United States once again significantly increased military and nuclear spending, while the Soviets were unable to respond and continued to pursue the détente . </P>

Who was winning the nuclear arms race by 1956