This article examines the political crisis of the last two years of the Soviet Union (1990–1991) through Bulgarian diplomatic documents and analytical memoranda. It focuses on how Bulgarian diplomats, observing events in real time, recorded the accelerating disintegration of the union state, formulated forecasts, and assessed alternative scenarios for reform. The article aims to reconstruct and interpret Bulgarian diplomatic conceptions of the causes and mechanisms of Soviet de-integration and to gauge the extent to which professional practice “neutralized the ideological filter” in their assessments. The study draws on internal correspondence of Bulgaria’s Ministry of Foreign Affairs, read against the unfolding political context in the USSR. Methodologically, it combines a problem-chronological framework with qualitative analysis of politico-diplomatic discourse: it isolates key causal clusters, ranks factors by perceived weight, and traces their articulation in specific episodes. The article shows that by December 1990 Bulgarian analysts had diagnosed a “threefold crisis” in the Soviet Union — political, economic, and international — and, despite a “high degree of unpredictability”, anticipated the USSR’s collapse a full year before it occurred. In the diplomatic record, the causes of disintegration are ordered by significance: political factors first, ideological second, and economic only third. Among the most consequential are an “administrative vacuum”, delays in drafting a new Union Treaty, the distinctive dynamics of multiparty pluralism as republican elites drift ed toward nationalism, and the breakdown of interrepublican ties. The article also examines proposed exit scenarios (a Union Treaty on Gorbachev’s model, a confederation, and an “enhanced presidential authority”), underscoring August 1991 as a catalyst of irreversible processes. The central conclusion is that, in Bulgarian assessments, the decisive mechanism of collapse was Russian-Union dual authority and “Russian separatism,” which institutionally set the RSFSR against the union center and hastened the finale — symbolically framed as a “Brest Agreement,” in deliberate allusion to Brest-Litovsk (1918).