Alexander Joseph, known as Alexander of Battenberg, was the first prince (knyaz) of the autonomous Principality of Bulgaria from 1878 until his abdication in 1886.

The Unification of Bulgaria was the act of unification of the Principality of Bulgaria and the province of Eastern Rumelia in the autumn of 1885. It was co-ordinated by the Bulgarian Secret Central Revolutionary Committee (BSCRC). Both had been parts of the Ottoman Empire, but the principality had functioned de facto independently whilst the Rumelian province was autonomous and had an Ottoman presence. The unification was accomplished after revolts in Eastern Rumelian towns, followed by a coup on 18 September [O.S. 6 September] 1885 supported by the Bulgarian Prince Alexander I. The BSCRC, formed by Zahari Stoyanov, began actively popularizing the idea of unification by means of the press and public demonstrations in the spring of 1885.