The inception of the third Bulgarian state dates back to March 3, 1878, following the conclusion of the Russo-Turkish war in San Stefano. Initially, the territory of the new state extended from the Black Sea to Lake Ohrid and from the Danube to the Aegean Sea, encompassing regions predominantly inhabited by Bulgarians. However, concerns among the Great Powers about the emergence of a large Balkan state prompted the Congress of Berlin to revise the borders. As a result, Mysia and the Sofia field were separated from Bulgaria and established as a vassal principality under Ottoman suzerainty, known as the Principality of Bulgaria. Meanwhile, the autonomous region of Eastern Rumelia, centered around Plovdiv, remained within the Ottoman Empire, effectively representing present-day southern Bulgaria. Macedonia, Odrin, and White Sea Thrace also remained under Ottoman control.
On September 6, 1885, the Union of Eastern Rumelia with the Principality of Bulgaria was proclaimed in Plovdiv, consolidating the territories under Bulgarian administration. Subsequently, on September 22, 1908, Bulgaria officially declared its legal independence from the Ottoman Empire.
