1890s: After centuries of rule by the Ottoman Turks, in 1878, northern Bulgaria becomes autonomous, and a united Bulgaria gains its independence in 1908.

Today: A German ally in both world wars, Bulgaria falls to Soviet domination during World War II and remains under its control until 1990. Upon signing of the European Constitution in 2004, Bulgaria is de facto considered a full-fledged member of the European Union. Bulgaria also joins NATO in 2004.

1890s: After becoming an autonomous principality in 1829, Serbia is recognized in 1878 as an independent country. In 1882, the ruling prince, Milan Obrenovi, is proclaimed king. Obrenovi establishes a liberal constitution, but his son Alexander, who rules from 1889 to 1903, rejects it, evoking hostility in Serbia until he is assassinated in 1903.

Today: From 1992 to 2002, Serbia and Montenegro are joined as the country of Yugoslavia. After 2002, the two states are in a loose federation, and a referendum in each...