Based on a series of controlled comparisons among regimes and states, Valerie Bunce's book argues that two factors account for the remarkable collapse of the socialist dictatorships in Europe from 1989-1992: the institutional design of socialism as a regime, a state and a bloc, and the rapid expansion during the 1980s of opportunities for domestic and international change. Together, these two factors explain not just why socialist regimes and states ended, but also why the process was peaceful in some cases and violent in others.
Bunce's work was revolutionary for the time of writing. This institutional framework and structural argument for the collapse of Yugoslavia, Czechoslovakia, and the USSR is persuasive. Of course, that does not rule out agency (the actions of Gorbachev, say).
Highly readable with a deep understanding of the region.