In Eastern Rumelia, where the Bulgarian population never ceased to protest against the division of the race, political life had developed on the same lines as in the principality. Among the politicians two parties had come into existence - the Conservatives or self-styled "Unionists," and the Radicals, derisively called by their opponents "Kazioni" or treasury-seekers; both were equally desirous of bringing about the union with the principality. Neither party, however, while in power would risk the sweets of office by embarking in a hazardous adventure. It was reserved for the Kazioni, under their famous leader Zakharia Stoyánoff, who in early life had been a shepherd, to realize the national programme. In 1885 the Unionists were in office, and their opponents lost no time in organizing a conspiracy for the overthrow of the governor-general, Krstovitch Pasha. Their designs were facilitated by the circumstance that Turkey had abstained from sending troops into the province. Having previously assured themselves of Prince Alexander's acquiescence, they seized the governor-general and proclaimed the union with Bulgaria (18th September). The revolution took place without bloodshed, and a few days later Prince Alexander entered Philippopolis amid immense enthusiasm.
His position now became precarious. The powers were scandalized at the infraction of the Berlin Treaty; Great Britain alone showed sympathy, while Russia denounced the union and urged the Porte to reconquer the revolted province - both powers thus reversing their respective attitudes at the congress of Berlin.
The Turkish troops were massed at the frontier, and Servia, hoping to profit by the difficulties of her neighbour, suddenly declared war (14th November). At the moment of danger the Russian officers, who filled all the higher posts in the Bulgarian army, were withdrawn by order of the tsar. In these critical circumstances Prince Alexander displayed considerable ability and resource, and the nation gave evidence of hitherto unsuspected qualities. Contrary to general expectation, the Bulgarian army, imperfectly equipped and led by subaltern officers, successfully resisted the Servian invasion. After brilliant victories at Slivnitza (19th November) and Tsaribrod, Prince Alexander crossed the frontier and captured Pirot (27th November), but his farther progress was arrested by the intervention of Austria (see Servo-Bulgarian War). The treaty of Bucharest followed (3rd of March 1886), declaring, in a single clause, the restoration of peace. Servia, notwithstanding her aggression, escaped a war indemnity, but the union with Eastern Rumelia was practically secured.
By the convention of Top-Khané (5th April) Prince Alexander was recognized by the sultan as governor-general of eastern Rumelia; a personal union only was sanctioned, but in effect the organic statute disappeared and the countries were administratively united. These military and diplomatic successes, which invested the prince with the attributes of a national hero, quickened the decision of Russia to effect his removal. An instrument was found in the discontent of several of his officers, who considered themselves slighted in the distribution of rewards, and a conspiracy was formed in which Tzankoff, Karaveloff (the prime minister), Archbishop Clement, and other prominent persons were implicated. On the night of the 21st of August the prince was seized in his palace by several officers and compelled, under menace of death, to sign his abdication; he was then hurried to the Danube at Rakhovo and transported to Russian soil at Reni. This violent act met with instant disapproval on the part of the great majority of the nation.
Stamboloff, the president of the assembly, and Colonel Mutkuroff, commandant of the troops at Philippopolis, initiated a counter-revolution; the provisional government set up by the conspirators immediately fell, and a few days later the prince, who had been liberated by the Russian authorities, returned to the country amid every demonstration of popular sympathy and affection. His arrival forestalled that of a Russian imperial commissioner, who had been appointed to proceed to Bulgaria. He now committed the error of addressing a telegram to the tsar in which he offered to resign his crown into the hands of Russia. This unfortunate step, by which he ignored the suzerainty of Turkey, and represented Bulgaria as a Russian dependency, exposed him to a stern rebuff, and fatally compromised his position. The national leaders, after obtaining a promise from the Russian representative at Sofia that Russia would abstain from interference in the internal affairs of the country, consented to his departure; on the 8th of September he announced his abdication, and on the following day he left Bulgaria.