Since the 1960s, the U.S. and Russia have prioritized bilateral negotiations on nuclear arms control. Even in times of conflict and tension, the two countries have known that cooperating on security and nuclear risk reduction is a life-or-death matter. However, this history of arms control diplomacy has recently come under threat.

Check out this timeline of U.S.-Russian arms control talks and treaties that have taken place since 1969, and why it is important to continue cooperation on further nuclear reductions following the extension of New START:

Strategic Arms Limitation Talks (SALT) I: Signed in 1972
Status: Superseded by SALT II; U.S. withdrew from ABM Treaty in 2002
SALT negotiations started in 1969 and culminated in 1972 with the signing of two documents: an Interim Agreement and the Anti-Ballistic Missile (ABM) Treaty. It was the first agreement between the United States and the Soviet Union that placed limits on their nuclear weapons arsenals.

The Interim Agreement capped U.S. and Soviet intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missile (SLBM) forces, and both sides agreed not to construct new ICBM silos and not to “significantly” increase the size of existing ICBM silos. SALT I was an interim agreement because the parties pledged to continue negotiations. The month before the agreement was due to expire, both the U.S. and Soviet Union stated that they would continue to honor the agreement while SALT II was being negotiated.

The ABM Treaty barred the two countries from deploying defenses against strategic ballistic missiles. In June 2002, the U.S. withdrew from the treaty, eventually deploying systems in Europe and spurring Russian modernization of its nuclear capabilities. Missile defense has become an obstacle to further progress on arms control negotiations.

Strategic Arms Limitation Talks (SALT) II: Signed in 1979
Status: Never entered into force; Expired in 1985; Followed by START I in 1991
SALT II talks took place from 1972 to 1979. The overarching goal of these talks was to replace the SALT I Interim Agreement with a more comprehensive, long-lasting treaty. The provisions of SALT II included banning new missile programs and limiting the number of multiple independently targetable reentry vehicles (MIRV) and long-range missiles to 1,320.

Although SALT II resulted in an agreement in 1979, the U.S. Senate did not ratify the treaty in response to the Soviet war in Afghanistan. The Soviet legislature also did not ratify it. The agreement expired on December 31, 1985 and was not renewed.

Intermediate-Range Nuclear Forces (INF) Treaty: Signed in 1987
Status: U.S. withdrew in 2019
After years of on and off negotiations, the INF Treaty was signed by U.S. President Ronald Reagan and Soviet General Secretary Mikhail Gorbachev in December 1987. The treaty required the two countries to eliminate all ground-launched missiles with a range of 500 to 5,500 kilometers. It was the first treaty to eliminate an entire class of nuclear weapons and marked the first time the two superpowers agreed to reduce their nuclear arsenals. In total, 2,692 missiles were eliminated.

The treaty led directly to another landmark treaty, the 1991 Strategic Arms Reduction Treaty (START). The U.S. formally suspended the INF Treaty in February 2019, and Russia did so on the following day in response. The U.S. formally withdrew from the treaty in August 2019.

Strategic Arms Reduction Treaty (START) I: Signed in 1991
Status: Expired in 2009; Followed by New START
The signing of the INF Treaty accelerated talks for START I, which was signed in July 1991 and entered into force in December 1994. The treaty prevented the two countries from deploying more than 6,000 warheads on top of 1,600 ICBMs and bombers. START I was a large and complex treaty, and led to reducing about 80 percent of strategic nuclear weapons at that time. Another important aspect of START I was its verification and transparency provisions, such as data exchange on strategic weapons and facilities and inspections.

START I expired in December 2009.

Strategic Arms Reduction Treaty (START) II: Signed in 1993
Status: Never entered into force
START II was meant to complement, rather than replace, START I. START II established a limit on strategic weapons, with reductions to be implemented in two phases. By the end of Phase I, the U.S. and Russia were to reduce their total deployed strategic nuclear warheads to 3,800-4,250, and by the end of Phase II, to 3,000-3,500. Phase II also required the elimination of all heavy ICBMs and all ICBMs on MIRVs.

However, the treaty never entered into effect. It was ratified by the U.S. Senate in January 1996 and by Russia in April 2000. Russia withdrew from the treaty in June 2002 in response to U.S. withdrawal from the ABM Treaty.

Strategic Offensive Reductions Treaty (SORT): Signed in 2002
Status: Superseded by New START
Signed in May 2002, SORT was in force from June 2003 until February 2011 when it was superseded by New START. Whereas START I limited warheads through their delivery systems, SORT limited operationally deployed warheads. Under SORT, both parties agreed to limit their nuclear arsenal to between 1,700 and 2,200 operationally deployed warheads each. It did not contain any verification measures. Instead, the U.S. and Russia agreed to rely on START I measures to ensure compliance.

After ratification by the U.S. Senate and the Russian State Duma, SORT came into force in June 2003. It would have expired on December 31, 2012 if not superseded by New START.

New Strategic Arms Reduction Treaty (START): Signed in 2009
Status: Still in effect, extended by the U.S. and Russia for five years in Jan 2021
In 2009, U.S. President Barack Obama and Russian President Dmitry Medvedev signed New START, a follow-up to START I which expired in December 2009. New START limits the two parties to 1,550 deployed nuclear warheads; 700 deployed ICBMs, deployed submarine-launched ballistic missiles, and deployed nuclear-capable bombers; and 800 total (deployed and nondeployed) launchers. It also provides for the inspections and data sharing on each other’s nuclear arsenals that had been lost when START I expired in 2009.

New START is working, and it’s imperative that Russia and the United States start negotiations for a follow-on agreement that continues decades of cooperation on nuclear arms reductions.