Signing "the Treaty of the Union of Sovereign States” failed after the August coup by conservative members and accelerated declarations of independence by Soviet Socialist Republics between August and December. Azerbaijan adopted its declaration of independence on 30 August 1991, before the dissolution of the Soviet Union on 26 December 1991; however Azerbaijan became part of the Commonwealth of Independent States later, in September 1993. By the end of 1991 fighting in Nagorno-Karabakh had escalated into a full-scale war, which culminated into a tense 1994 cease-fire that has persisted into the 21st century. Although a cease-fire was achieved, several escalations over the years such as in 2016 and in 2020 had resulted in large-scale military confrontations.