Bulgaria is celebrating on Monday the 125th anniversary since the unification of the Principality of Bulgaria and Eastern Roumelia.

Bulgaria's President Georgi Parvanov together with Parliamentary Speaker Tsetska Tsacheva are to attend the official ceremony held at the city of Plovdiv this evening.

After the medieval Bulgarian empire was conquered by the Ottoman Turks in 1396 AD, Bulgaria was formally restored as a nation-state on March 3, 1878, after the Russian-Turkish War of 1877-78.

Under the San Stefano peace treaty between Russia and Ottoman Turkey, Bulgaria was set up as a state on a territory of 170 000 square kilometers encompassing the three historic-geographic regions traditionally inhabited by Bulgarians - Moesia, Thrace, and Macedonia.

Three months later, in July 1878, the Great Powers from the so called "European Concert" revised the San Stefano Treaty in the so called Berlin Congress, an outcome of their conflicting great power interests. As a result, the Principality of Bulgaria was set up in most of Moesia and the Sofia region on a territory of 63 000 square km. About half of Thrace, or Southern Bulgaria was made an autonomous Ottoman Province called Eastern Roumelia, with a territory of 36 000 square km. The rest of the Bulgarian lands under the Berlin Treaty - including all of Macedonia and half of Thrace - were left in the Ottoman Empire.

Bulgaria's entire political and social life in 1878-1944 was marked by the desire to unify all Bulgarian-populated lands in one nation state - leading the country to participate in five wars in that period. The Unification of the Principality of Bulgaria and Eastern Roumelia at the time was hailed as a crucial and successful but only a partial step towards this goal.

On September 6, 1885, the Principality of Bulgaria unified with the autonomous Ottoman province of Eastern Roumelia, a few years after its liberation from Ottoman yoke.

The historic proclamation was made after a march by a handful of Bulgarians from the small town of Saedinenie  ("Unification") to the town of Plovdiv, removing one of the gravest injustices imposed in the wake of the Berlin Congress. The Unification was prepared by a network of secret revolutionary committees in Eastern Roumelia, and was backed by the then Bulgarian ruler, Knyaz (King) Alexander I Batenberg.

Great Britain had been the primary protagonist in downsizing Bulgaria during the Berlin Congress because it feared a large Bulgarian state with access to the Mediterranean would be under Russian influence. However, in 1885-1886, it backed informally but rather noticeably, Bulgaria's Unification, seeing that the Russian Empire at the time was against this move, which stirred diplomatic tension in the Balkans, and seized the chance to demolish Russian influence in Bulgaria.

As other Balkan countries objected to Bulgaria's Unification, Serbia attacked Bulgaria in November 1885. In a grand national effort to defend the Unification, the young Bulgarian Army, which had just been left by its senior Russian officers, repulsed the attack, and defeated the Serbs on their territory, thus making the Unification of Northern and Southern Bulgaria a fait accompli.

But it was not until 1886 when the Great Powers recognized the almost doubled state of Bulgaria with a Bulgarian-Ottoman treaty.

After the Unification of 1885, Bulgarian efforts were focused on making Macedonia and the rest of Thrace part of the country. Thus, Bulgaria backed the VMORO (Internal Macedonian-Adrianople Revolutionary Organization) and its staging of the failed Ilinden-Preobrazhenia Uprising in 1903, and subsequently took part in the Balkan Wars of 1912-1913, World War I (1915-1918) and World War II (1941-1945).

The celebrations of Bulgaria's Unification Day are traditionally held the night of September 6 in Plovdiv, the city which once was the capital of the Ottoman province of Eastern Roumelia invented by the European Great Powers at the Berlin Congress in July 1878.