Updated March 2021
The Anti-Ballistic Missile (ABM) Treaty was an agreement between the United States and the Soviet Union that limited the number of ground-based anti-ballistic missile systems and sites that each side could have. Both parties also agreed not to develop sea-based, air-based, or space-based ABM systems. After the fall of the Soviet Union, the treaty was expanded to include Belarus, Ukraine and Kazakhstan.
The ABM Treaty was signed in May 1972 and entered into force in October of that year. Under the treaty, the United States and the Soviet Union could establish two ABM sites: one to protect the national capitol and one to protect an ICBM launch site. The sites, each of which could have a maximum of 100 interceptors and 100 launchers, were required to be at least 807 miles (1,300 kilometers) apart to prevent the creation of a regional defense zone. The treaty did not limit the number of early warning radars that each country could deploy, but stipulated that future radars be located on the countries’ borders facing outwards.
In 1974, a Protocol to the Treaty was added to limit each side to only one ABM site.
Under the treaty, each member could verify other parties’ compliance using national technical means of verification, such as satellite reconnaissance.
The treaty also created a Standing Consultative Commission (SCC), a forum where each country was represented by a Commissioner, Executive Officer and delegation. The SCC could not impose sanctions or any other repercussions on parties that violated the treaty; instead it served as a forum in which members could raise concerns about other’s compliance. The SCC served as a vital body within which the United States and the Soviet Union remained in communication even when other diplomatic initiatives broke down.
In December 2001, the George W. Bush Administration announced that the United States planned to withdraw from the ABM Treaty. Six months later, the United States officially withdrew from the treaty in order to develop and deploy the Ground-Based Midcourse Defense (GMD) system. At the time, this was the only time that the United States had withdrawn from a major international arms control treaty. Russia said that it did not feel threatened by U.S. withdrawal, but called the move “a mistake.”
Why It Mattered
The ABM Treaty was part of the U.S.-Soviet effort to control the arms race in the 1970s. It was negotiated as part of the Strategic Arms Limitation Talks (SALT I) that established limits for strategic offensive weapons.
The ABM Treaty codified the U.S.-Russian understanding that offensive weapons and defensive systems are linked. If a country develops an ABM system, an adversary could be incentivized to build more offensive weapons to overwhelm the defensive system. That would lead to an arms race.
Until the United States withdrew from the ABM Treaty, it contributed to strategic stability and helped create the dynamic under which further reductions of U.S. and Soviet nuclear arsenals were possible.