On December 5, 1994, leaders of the United States, the United Kingdom, and the Russian Federation met in Budapest, Hungary, to pledge security assurances to Ukraine in connection with its accession to the Treaty on the Nonproliferation of Nuclear Weapons (NPT) as a non-nuclear-weapons state. The signature of the so-called Budapest Memorandum concluded arduous negotiations that resulted in Ukraine’s agreement to relinquish the world’s third-largest nuclear arsenal, which the country inherited from the collapsed Soviet Union, and transfer all nuclear warheads to Russia for dismantlement. The signatories of the memorandum pledged to respect Ukraine’s territorial integrity and inviolability of its borders, and to refrain from the use or threat of military force. Russia breached these commitments with its annexation of Crimea in 2014 and aggression in eastern Ukraine, bringing the meaning and value of security assurance pledged in the Memorandum under renewed scrutiny.
Budjeryn, Mariana, and Matthew Bunn. "Budapest Memorandum at 25: Between Past and Future." March 2020.