Slavs have lived in the area of Montenegro since the 6th and 7th centuries in the medieval state of Duklja. By the 14th century, the mountains behind the Gulf of Kotor were coming to be referred to as "Montenegro" (Montenegrin: "Crna Gora"; literally translates as “Black Mountain”), and by the 15th century, the name was coming to increasingly replace the older name, Zeta. Since the end of the 17th century, Montenegro existed as a de facto independent country, first as a theocratic Prince-Bishopric (1694–1852), then as a secular Principality (1852–1910) and finally as a Kingdom (1910–1918). After the end of World War I, Montenegro was incorporated into the Kingdom of Yugoslavia, thus losing its statehood. This led to a short-lived Christmas Uprising of 1919, between supporters of Petrović-Njegoš dynasty and Montenegrin statehood and proponents of unification with Serbia and Yugoslavia under the Karađorđević dynasty. After the World War II, Montenegro regained its political sovereignty, becoming one of the six constituent republics of the SFR Yugoslavia, and Montenegro's sovereignty was recognised once again. A portion of Montenegrins declares as ethnic Serbs, while a larger proportion of citizens of Montenegro identifies ethnically as Montenegrin, a division that was exacerbated with the fall of socialism. This division has deepened further since the movement for full Montenegrin independence from the Federal Republic of Yugoslavia began to gain ground in 1991, while full independence was regained after the 2006 referendum.