Communist one-party state proclaimed after the September 1946 referendum abolished the monarchy; a Warsaw Pact member closely aligned with the Soviet Union under Todor Zhivkov's long rule (1954-1989).
Communist rule ended with Zhivkov's ouster in November 1989; the country was renamed the Republic of Bulgaria in 1990, matched by modern Bulgaria (Q219) starting 1990 per the atlas's existing record.
Covers Balkan political history from 1878 onward, spanning Bulgaria's autonomous principality and its later communist republic.