On Orthodox Christmas, January 7, 1919, a national uprising occurred in Montenegro. The catalyst was the decision of the unconstitutional "Grand National Assembly" (Podgorička skupština) for annexation by Serbia. The Christmas Uprising resulted in a war of Montenegrins against the Serbian occupation that lasted until 1926.

This uprising might have taken a different course had King Nikola not been deceived by the Great Powers, who promised (a promise never fulfilled) to reestablish the sovereign state of Montenegro by diplomatic means if he would stop supporting the uprising. Based on this promise, he issued a proclamation in January 1919 asking for a stop to the resistance.

The core of the resistance was crushed in a severe, comprehensive military campaign in 1922-23, but guerrilla resistance continued in the highlands for several more years.

An estimated three thousand Montenegrins lost their lives, and another three thousand were wounded; several thousand homes were burned and destroyed. The already large emigration, particularly to the United States, accelerated. At that time, Montenegro was a country of only 300,000.

The Christmas Uprising, about which new historical documents are now being published for the first time since the 1920s, shows that Montenegro's entry into Yugoslavia was forced and illegitimate, in a fashion similar to the Soviet annexation of the three Baltic states.