Uprisings against Ottoman control in 1875 and 1876 began military action that finally brought Bulgaria conditional independence in 1878. Bulgaria was a major battleground in the Russo-Turkish War of 1877-78. Russia fought the war as the champion of Slavs living under the Ottoman Empire in the Balkans. Under the Treaty of San Stefano, signed March 3, 1878, Bulgaria became an autonomous state under Russian protection. The same year, the European powers forced Bulgaria to sign the Treaty of Berlin, returning substantial territory to the Ottoman Empire in the name of regional balance, but Bulgaria retained its autonomy.

Conflict with Balkan neighbors began when the new nation sparked a brief war with Serbia in 1885 over control of the province of Eastern Rumelia. Seeking compensation for Bulgaria's annexation, Serbia invaded the province and was defeated by Prince Alexander, modern Bulgaria's first ruler. After inconclusive fighting, Bulgaria and Serbia agreed to the Treaty of Bucharest, which restored prewar borders in 1886.

During the twentieth century, persistent territorial disputes and dissatisfaction with borders determined Bulgaria's position in four wars. In 1912 Bulgaria entered the Balkan League, a military alliance with Serbia and Greece, to eliminate the last vestiges of Turkish rule in the Balkans and to expand its own territory in the process. Fielding approximately 180,000 troops, Bulgaria provided the bulk of the military personnel for operations against Turkish forces in the First Balkan War. Bulgarian armies besieged Constantinople in November 1912, but they were driven back temporarily by the Turks. When the key city of Adrianople fell to Bulgarian and Serbian forces in March 1913, Turkey capitulated. It surrendered its European possessions under the Treaty of London in May 1913.

A dispute over the spoils of the First Balkan War led directly to the Second Balkan War. Bulgaria asserted that Serbia occupied more of Macedonia and Thessaloniki than it was allowed by the prewar agreement. In June 1913, Bulgarian armies attacked Serbian forces in Macedonia and another army advanced into Thessaloniki. After checking this offensive, Serbian and Greek forces pushed the Bulgarians back into Bulgaria in July. Romania then declared war on Bulgaria and advanced unopposed toward Sofia, while Turkey capitalized on the situation to retake Andrianople. Bulgaria sued for peace and lost territory in Macedonia, Thrace, and Southern Dobrudja to Greece, Serbia, and Romania respectively in the Treaty of Bucharest (August 1913).

Bulgaria's rivalry with Serbia and Greece defined its participation in World War I. Bulgaria avoided involvement in the war until 1915 when it mobilized 1.2 million soldiers and joined the Central Powers in attacking Serbia. Bulgaria took this action in the expectation that a victory by the Central Powers would restore Greater Bulgaria. In October 1915, two of Bulgaria's armies drove west into Serbia while allied Austro-Hungarian and German armies drove south. Bulgarian forces blocked British and French troops in The6fa hessaloniki from linking with Serbian forces.

In mid-1916 over 250,000 British, French, and Serbian troops prepared for an offensive from Thessaloniki northwest along the Vardar River. Although the Germans and Bulgarians preempted the offensive and drove this force beyond the Struma River by late August, the war then settled into a long, costly stalemate along the Vardar. Seriously weakened by a poor military supply system and widespread unrest among the soldiers, Bulgaria collapsed and surrendered in 1918. The country suffered greatly during the war. Mobilization disrupted food production, and German requisitioning of grain and other foodstuffs taxed stored food supplies. About 100,000 Bulgarian soldiers were killed in combat, and 275,000 noncombatants died as a direct result of the war (see World War I , ch. 1).

Data as of June 1992