Bulgaria
Bulgaria occupies a portion of the eastern Balkan peninsula, bordering five countries—Greece and Turkey to the south, Macedonia and Serbia to the west, and Romania to the north. The land borders have a total length of , and the coastline has a length of . Its total area of ranks it as the world's 105th-largest country. Bulgaria's geographic coordinates are 43° N 25° E. The most notable topographical features are the Danubian Plain, the Balkan Mountains, the Thracian Plain, and the Rhodope Mountains. The southern edge of the Danubian Plain slopes upward into the foothills of the Balkans, while the Danube defines the border with Romania. The Thracian Plain is roughly triangular, beginning southeast of Sofia and broadening as it reaches the Black Sea coast.
Balkan Federation
The concept of a Balkan federation emerged in the late 19th century from among left political forces in the region. The central aim was to establish a new political unity: a common federal republic unifying the Balkan Peninsula on the basis of internationalism, socialism, social solidarity, and economic equality. The underlying vision was that despite differences among the Balkan peoples the historical need for emancipation was a common basis for unification.