The Principality of Montenegro was a principality in Southeastern Europe that existed from 13 March 1852 to 28 August 1910. It was then proclaimed a kingdom by Nikola I, who then became King 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 lasted, through various successor states, for almost 88 years, ending in 2006.