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.
Greek–Serbian Alliance of 1867
In the middle of the 19th century, most of the territory of Balkans was still part of the Ottoman Empire, with several newly established independent or autonomous entities like Serbia and Greece. All of them struggled to expand their influence and territory at Ottoman expense. Their intention was strongly opposed by Austria who opposed development of Balkan nations and revolutions in the Ottoman provinces of Europe ("Rumelia"). Napoleon III was the champion of the idea of Balkan nationalism and fostered Serbia and Greece to build alliances and undermine Ottoman influence in the region. France planned to resolve the Balkan Eastern Question through gathering of all Balkan Slavic people, including Bulgarians, around Serbia as their pillar. This was not only informally suggested by French diplomats since 1861, but also formally proposed in Saint Petersburg in 1867. The establishment of Balkan alliances was supported and aided by Russia because it corresponded with its policy of promoting Balkan unity.