The Strategic Arms Reduction Treaty I (START I) was the first treaty that required U.S. and Soviet/Russian reductions of strategic nuclear weapons. It was indispensable in creating a framework that ensured predictability and stability for deep reductions.
The dissolution of the Soviet Union caused a delay in the entry into force of the treaty, as the classification of states as nuclear or non-nuclear had to be determined, among other things. Reductions of nuclear weapons had to be completed within seven years after entry into force and maintained for another eight years. States were verified by on-site inspections. Both the United States and the Russian Federation continued reduction efforts.
Opened for Signature: 31 July 1991
Entry into force: 5 December 1994
Implementation Deadline: 5 December 2001
Expiration: 5 December 2009
Official Text: https://media.nti.org/documents/start_1_treaty.pdf
ACA Backgrounder: https://www.armscontrol.org/factsheets/start1