Although I know what you mean, Bulgaria is not a Third World Country. I think a better term would be Developing Country [0]. Third world means that it wasn't allied with either the USA/UK (First World) or Russia/China (Second World) during the Cold War [1]. Bulgaria was part of the Eastern Bloc [2].
[0] http://en.wikipedia.org/wiki/Developing_country
[1] http://en.wikipedia.org/wiki/Third_World
[2] http://en.wikipedia.org/wiki/Eastern_Bloc#Bulgaria