This is a map of the countries that used to belong to the Soviet Union. The Soviet Union was created when the Red Army defeated the White Army, overthrew the Russian Emperor, and established a socialist dystopia. After the fall of communism several areas of the former Empire/Union became independent nations. Thus, there are several former communist nations that used to be a part of the Soviet Union.
However, Bulgaria was not one of those. Bulgaria was part of a group of several nations that were placed under the control of the Soviet Union after World War II. Like any good dystopia, the Soviet Union was eager to export their tyranny to their neighbors. Those countries, along with the USSR made up the Communist Bloc seen below.
What is the difference? Quite significant actually. Think of it this way, Canada is part of the British Commonwealth. However, it is not part of Great Britain. Should Canada leave the Commonwealth it would not cause Great Britain to split into different countries. In the same way, Bulgaria, Poland, Romania, Czechoslovakia, Hungary, Yugoslavia, East Germany, and Albania were part of the Bloc, but they were not a part of the USSR. It would have been theoretically possible for them to overthrow socialism and yet have had the USSR remain intact. There is confusion because the time between freedom coming to Eastern Europe and the dissolution of the Union happened so close together historically that they seem to be one in the same event.
In 1989 Eastern Europe did indeed receive independence from the Soviet Union. However they were never a part of the USSR. They were subjected to a puppet dictatorship under the control of the Soviet Union. They were not the same country, and now, thanks to the freedom loving people of the world, they never will be.
