Montenegro suffered severely in World War I. At the first invasion of Serbia by the Austrian armies, Montenegro lost no time in declaring war against the Central Empires. Although the army numbered only about 40,000 men, they were at once placed in the field. A separate army was dispatched by Austria to invade Montenegro and to prevent a junction of the Serbian and Montenegrin armies. This force, however, was repulsed, and from the top of the strongly fortified Mount Lovcen, the Montenegrins carried on the bombardment of Cattaro held by the enemy. On August 10, 1914, the Montenegrin infantry delivered a strong attack against the Austrian garrisons, but they were unable to make good the advantage they first gained. They successfully resisted the Austrians in the second invasion of Serbia and almost succeeded in reaching Sarajevo in Bosnia. With the beginning of the third invasion, however, they were compelled to retire before greatly superior numbers, and Serbia was finally overrun by Austro-German armies. Montenegro was also invaded (January 1916) and for the remainder of the war was in the possession of the Central Powers.
King Nicholas fled to Italy and then to France; the government was tranferred to Bordeaux. Montenegro was eventually liberated from the Austrians by the forces of Serbia. A newly convened National Assembly of Podgorica (Podgorička skupština), supervised by Serbian forces, accused the king of seeking a separate peace with the enemy and because of that deposed him, followed by a ban on his return. Montenegro was subsequently annexed to or united with Serbia on November 29, 1918.