Celebrations have begun Monday across the country with Bulgaria marking 106 years since the formal declaration of its independence from the Ottoman Turkish Empire.

Even though the third Bulgarian state was technically restored in 1878, for the first 30 years of its existence it was a tributary principality to Ottoman Turkey, until complete independence was achieved on September 22, 1908.

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, as a result of the Russian-Turkish War of 1877-78 brought about by the bloodily crushed April Uprising of 1876.

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. The Principality of Bulgaria was a vassal state, while Eastern Roumelia was technically an Ottoman province.

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. First, the Unification of the Principality of Bulgaria and Eastern Roumelia in 1885, and the declaration of full independence in 1908 were hailed as crucial and successful but only partial steps 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 Ilinden-Preobrazhenia Uprising in 1903 and several other revolts in then European Turkey in that period.

As the uprisings of the Bulgarian populations in Thrace and Macedonia failed, the Bulgarian leadership decided the only way help its compatriots still living under Ottoman rule was to wage a war against Ottoman Turkey. To do this, Bulgaria had to be able to enter international alliances, and to declare war as a sovereign nation state.

Thus, the Bulgarian Cabinet and ruler declared the country's independence on September 22, 1908, in a historic ceremony in one of the nation's medieval capitals Veliko Tarnovo. They used the fact that one of the European Great Powers broke the Berlin Treaty – Austria-Hungary had declared the annexation of Bosnia and Herzegovina, which it was supposed to rule for a period 30 years, under the Treaty.

The actions of the Bulgarian leaders were in fact coordinated with those of the emperor and government in Vienna. Austria-Hungary announced the annexation of Bosnia and Herzegovina the following day, ushering into the Bosnian Crisis (or Annexation Crisis) of 1908-1909 creating diplomatic tension among the Great Powers that served as a preview of the Bosnian or Sarajevo Crisis of 1914 leading to the breakout of World War I.

Thus, as a result of Bulgaria's declaration of independence, the Bulgarian ruler Ferdinand I, who until then had been a Knyaz (the Slavic equivalent of "King"), became a Tsar (technically the Slavic title for emperor). Under international diplomatic pressure, Ottoman Turkey reacted to Bulgaria's declaration of independence only with diplomatic protests, without military action.

As it became independent, Bulgaria subsequently took part in the Balkan Wars of 1912-1913, World War I (1915-1918) in seeking to regain all of its national territory (and in World War II (1941-1945)), being ultimately unsuccessful.

The celebrations of Bulgaria's Independence Day are traditionally held the night of September 22 in Veliko Tarnovo, the capital of the Second Bulgarian Empire that in 1908 Tsar Ferdinand and Prime Minister Alexander Malinov chose as the site for the proclamation of independence.

The Independence Day has been celebrated as an official public holiday since a decision of the Bulgarian Parliament from September 10, 1998.