The revolution of Plovdiv (18 September 1885), which brought about the union of Eastern Rumelia with Bulgaria, took place with Alexander's consent, and he at once assumed the government of the province. In the year which followed, the prince gave evidence of considerable military and diplomatic ability. He rallied the Bulgarian army, now deprived of its Russian officers withdrawn by Tsar Alexander III which Alexander replaced by graduates of the Bulgarian Military Academy to resist the Serbian invasion (later on called "The Victory of Bulgarian Cadets vs. Serbian Generals"). The Bulgarians won a decisive victory at Slivnitsa (19 November), which Alexander had little to do with, having arrived in after the battle was already over. He pursued King Milan of Serbia into Serbian territory as far as Pirot, which he captured (27 November). Although the intervention of Austria protected Serbia from the consequences of defeat, Prince Alexander's success sealed the union with Eastern Rumelia, and after long negotiations the sultan Abdul Hamid II nominated the Prince of Bulgaria as governor-general of that province for five years (5 April 1886).