One of the main points of the 1968 Nuclear Non-Proliferation Treaty was the requirement that those states which currently possessed nuclear weapons work towards nuclear disarmament. The two world super powers at the time, the United States and the Soviet Union both possessed nuclear arsenals. The U.S. possessed about one thousand inter-continental ballistic missiles (ICBMs) and about six hundred and fifty submarine launched ballistic missiles (SLBM) in 1969. The Soviets had around one thousand ICBMs as well hundreds of SLBMs in 1969.
By that time, the Soviets had installed an anti-ballistic missile system (ABM) around their capital, Moscow, Russia. The U.S. had announced plans to protect twelve sites but only built one ABM system to protect a missile base in North Dakota. The U.S. and the Soviets were also working on warheads that contained multiple nuclear bombs. These multiple independently targetable reentry vehicles, referred to as MIRVs, were a response to the work on anti-ballistic missile systems (ABMs).
These new developments in the nuclear arms race between the U.S. and the Soviets increased international pressures for work towards nuclear disarmament. The first round of Strategic Arms Limitation Talks known as SALT I began in Helsinki, Finland in late 1969. These bilateral disarmament talks between the U.S. and the Soviets went on for two years of hard negotiating at meetings which were held alternately in Helsinki, Finland and Vienna, Austria.
The Soviets wanted to negotiate over U.S. bombers in Europe while the U.S. wanted to negotiate over Soviet mid-range nuclear weapons aimed at Europe. Both sides dropped these positions in favor of only negotiating an interim agreement on ICBMs and ABMs.In May of 1972, Richard Nixon and Leonid Brezhnev signed two agreements, one to deal with anti-ballistic missile systems and another dealing with limiting strategic nuclear weapons.
The Anti-Ballistic Missile Treaty limited both sides to having only two site protected by ABM systems. The U.S. dismantled their single ABM system a few years later. The ABM system around Moscow is still in use.
The other treaty signed by the U.S. and the Soviets as a result of the talks was called the Interim Agreement Between The United States of America and The Union of Soviet Socialist Republics on Certain Measures With Respect to the Limitation of Strategic Offensive Arms. This agreement was to be in force for five years. Strategic ICBMs were to be frozen at 1972 numbers. No new ICBM silos could be built. Signatories were allowed to build new SLBMs if their number was balanced by a equal reduction in the number ICBMs. Some allowance was made for modernizing launchers.
The U.S. had basically frozen its missile deployment program during the talks while the Soviets added 50% to their ICBM numbers and quadrupled their SLBMs.
Start of the SALT I negotiations from NATO photo archive:
