Kingdom of Montenegro

The Kingdom of Montenegro was a monarchy in southeastern Europe, present-day Montenegro, during the tumultuous period of time on the Balkan Peninsula leading up to and during World War I. Officially it was a constitutional monarchy, but absolutist in practice. On 28 November 1918, following the end of World War I, with the Montenegrin government still in exile, the Podgorica Assembly proclaimed unification with the Kingdom of Serbia, which itself was merged into the Kingdom of Serbs, Croats and Slovenes three days later, on 1 December 1918. This unification with Serbia would last, through various successor states, for almost 88 years, until finally coming to an end in 2006, when Montenegro regained its independence.

Trivia

 * The official language of the Kingdom of Montenegro was Serbian. Montenegro's own language, Montenegrin, didn't become a separate language from Serbian until the breakup of Yugoslavia, and Montenegrin became the official language of Montenegro when it became independent from Serbia in 2006.