The word "unification" embodies thoughts of joy, external support, celebration and a positive future outlook. For Bulgaria, when the Principality of Bulgaria and the semi-autonomous Ottoman province of Eastern Rumelia were united in the autumn of 1885, this was not entirely the case.

The two were part of the three into which the Bulgarian territories were split after the Treaty of Berlin in 1878.

The treaty had provided the Principality of Bulgaria with a capital at Veliko Turnovo and the semi-autonomous Ottoman Eastern Rumelia with a capital at Plovdiv. The third territory was Macedonia, which remained under Ottoman control.

These three lands had first made attempts at reunification in 1880, and received support from the new British prime minster William Gladstone, but not from the nation he was leading. Ottoman events external to Bulgaria, Eastern Rumelia and Macedonia proper also dissuaded these efforts.

About five years later, activists in Eastern Rumelia turned to think it better to put off preparations for a revolution in Macedonia, and focus on the reunification of only the Principality of Bulgaria and Eastern Rumelia. Alexander Battenberg, head of state of the Principality of Bulgaria, supported the move, seeing it as a hope for political survival among his worsening relations with Russia.

On September 6 1885, after several days of riots initiated by Bulgarians, the Bulgarian Secret Central Revolutionary Committee, led by Zahari Stoyanov, announced in Plovdiv the unification of the two territories.

This action contradicted the will of the Austro-Hungarian Empire, France, Germany, Greece, Serbia and especially Russia. However, as the first independent act of the reborn country, it had huge support among the Bulgarians. Battenberg expected a possible assault from the Ottoman Empire and had deployed most of his troops to the south border. A surprising turn of events followed.

The Austro-Hungarian Empire was particularly worried about the course events were taking (it was in the process of expanding its own influence in the Balkans), so it encouraged Serbia to attack the fledgling Bulgarian state, promising territorial gains in return for concessions in the western Balkans. Bulgaria, at the time, made efforts to avoid Serbian intervention. A delegation was sent to Serbia to convince king Milan Obrenovic IV, married to Austrian grand duchess Natalia, to remain neutral, but he was determined to have his part in the action. After receiving 250 million dinars from Vienna, Serbia launched its campaign against Bulgaria on November 2. The pretext for the campaign was that the Unification had created a very large Bulgaria, upsetting the balance of power in the Balkan Peninsula.

The Serbs had a total of 70 000 soldiers with 500 guns, and military experience from the Serbo-Turkish war in 1876 and the Russo-Turkish war in 1877-78. Against them, Bulgaria had only 10 000 soldiers on its western border, since most of the army was awaiting and un-realised Turkish assault from the south, and no officers ranking higher than captain: after the Unification of Bulgaria, Russian emperor Alexander III issued a decree to recall the Russian military officers from the Bulgarian army. Given these circumstances, it was widely expected that the 70 000-strong Serbian army with its experience would soon reach the Bulgarian capital and defeat Bulgaria.

With the odds stacked against it, Bulgaria had to immediately redeploy its 128 000 troops from the southern to the western border. The only railroad available at the time was that to Belovo, only one third of the distance to Sofia. The rest of the distance the army had to cover on foot in terrible weather conditions. Normally it would have taken 10 days for a person to cover the distance; Bulgarian soldiers made it an unprecedented three days. By November 5, the Serbian troops had already advanced to the town of Slivnitsa, only 30km from Sofia.

The Serbs launched their offensive on November 6, but despite the numerical supremacy of the enemy, the Bulgarians managed to hold their positions and repelled Serbian attacks. At one point, left without munitions, Bulgarian soldiers started to prepare for hand-to-hand combat.

Despair grew as they saw numerous enemy troops at the rear and fears circulated that a Serbian column had besieged them.

When all seemed lost, the column echoed with the song Shoumi Maritsa (Maritsa Flows Bloody Waters), later the first Bulgarian national anthem. It was the first 32 000 troops arriving from the Turkish border. Soaked, hungry and with torn boots, some barefoot, they joined the battle and drove the Serbs away from Slivnitsa.

Bulgaria's counterattack was launched and the Serbs were defeated near Dragoman and then in Pirot, on their own territory. On November 16 Count Kevenhuler, the Austro-Hungarian ambassador to Serbia, went to Bulgarian army headquarters and demanded the end of all military actions, warning Bulgaria that if its army did not retreat, the Austro-Hungarian Empire would enter the conflict. He also warned Battenberg that this might give Russia a reason to occupy Bulgaria and that he could lose his throne. Desired result achieved, all actions of the Bulgarian army in Serbia were ceased and negotiations started.

On February 19 1886 the peace treaty between Bulgaria and Serbia was signed in Bucharest. The war lasted about two weeks and ended without territorial changes and reparations. It was the shortest war in the Balkans and had the least bloodshed, with only 700 killed on each side. It proved priceless for Bulgaria; the September 6 Unification has remained subsequently undisputed.