I think Bulgaria has enjoyed such a long history as a sovereign country is because of it's trade routes. The economy was always very viable.
Bulgaria, (click here) officially Republic of Bulgaria, Bulgarian Republika Bŭlgariya, country occupying the eastern portion of the Balkan Peninsula in southeastern Europe. Founded in the 7th century, Bulgaria is one of the oldest states on the European continent. It is intersected by historically important routes from northern and eastern Europe to the Mediterranean basin and from western and central Europe to the Middle East. Even before the creation of the Bulgarian state, the empires of ancient Rome, Greece, and Byzantium were strong presences, and people and goods traveled the land with frequency....
...Nearly rectangular in outline, Bulgaria is bounded by Romania to the north, with most of the border marked by the lower Danube River. The Black Sea lies to the east, Turkey and Greece to the south, Macedonia to the southwest, and Serbia to the west. The capital city, Sofia, lies in a mountainous basin in the west....
