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.

In diplomatic history, the Eastern question was the issue of the political and economic instability in the Ottoman Empire from the late 18th to early 20th centuries and the subsequent strategic competition and political considerations of the European great powers in light of this. Characterized as the "sick man of Europe", the relative weakening of the empire's military strength in the second half of the eighteenth century threatened to undermine the fragile balance of power system largely shaped by the Concert of Europe. The Eastern question encompassed myriad interrelated elements: Ottoman military defeats, Ottoman institutional insolvency, the ongoing Ottoman political and economic modernization programme, the rise of ethno-religious nationalism in its provinces, and Great Power rivalries. In an attempt to triangulate between these various concerns, the historian Leslie Rogne Schumacher has proposed the following definition of the Eastern Question:The "Eastern Question" refers to the events and the complex set of dynamics related to Europe's experience of and stake in the decline in political, military and economic power and regional significance of the Ottoman Empire from the latter half of the eighteenth century to the formation of modern Turkey in 1923.