Macedonia, however, remained an issue for Bulgaria. In World War I Bulgaria succeeded in invading Macedonia. During the interwar period Macedonia was divided between Greece, Bulgaria, and Yugoslavia, Yugoslavia retaining the largest portion of the land. In the 1923-34 period Macedonian terrorism plagued the country and wreaked havoc on Bulgarian political and social life. During World War II the Bulgarians invaded both Greek Macedonia and Yugoslav Macedonia once again. Although the Macedonians themselves were divided in their sentiments between loyalties to Greeks, Yugoslavs, and Bulgarians, the land eventually reverted to Yugoslavia during World War II. As an issue, however, it still burns in the minds of the Bulgarians. The Macedonian question has been aptly referred to as "that eternal Balkan sore spot of rival nationalism."
WORLD WAR I
As was the case in the Balkan wars, Bulgaria's primary motivation for engagement in World War I was irredentism. Again the country was determined to regain the two lands that had escaped her grasp in the past: Macedonia and Thrace. Although Macedonia was prized for political and social reasons, Thrace represented a strategically more significant objective. In order to develop foreign trade, Bulgaria required an outlet to the sea; Thrace represented that outlet.
The domestic situation in the country before World War I was mixed. Although Bulgaria's army had been demobilized at the end of the Second Balkan War (1913) and economic conditions were rapidly improving, the mood of the monarchy and the middle class was one of vindictiveness and retaliation against those countries that had stripped Bulgaria of its territories. The country became divided between those who wanted closer relations with Russia and the Triple Entente and those who preferred an alliance with the Central Powers. As the war neared, the struggle between these camps intensified.
Bulgaria, of all the Balkan states, was the only one to join the Central Powers, led by Germany and Austria, in World War I. It was deeply ironic that Bulgaria chose to side with her former enemy and oppressor, Turkey, and against her former friend and protector, Russia. Again, the issue for Bulgaria was the Macedonian question. Serbia and Greece, which had triumphed over Bulgaria in the Second Balkan War, were allied with the entente powers. Bulgaria chose to fight against these enemies in order to regain Macedonia. Although the entente powers hoped to woo Bulgaria to their side, they refused—because of Serb and Greek pressures—to cede Macedonia to Bulgaria. The Central Powers, on the other hand, who were already at war with Serbia, were willing to promise Macedonia to the Bulgarians in exchange for their collaboration.
In the early stages of the war Germany won victories in France and on the eastern front. Although the government then ruling Bulgaria was already inclined to join the Central Powers, these early successes made German promises even more appealing. In August 1915 a secret treaty of alliance was signed by Bulgaria and Germany, containing a clause that promised Serbian, Greek, and Romanian territories to the Bulgarians. Thus the quadripartite alliance was born, composed of Germany, Austria-Hungary, Turkey, and Bulgaria.
By September 1915 Bulgarian troops were mobilized and began to deploy along the borders of Greece and Serbia. On October 1, 1915, Bulgaria declared war on Serbia and, with the assistance of Austrian and German troops, succeeded in defeating the Serbian army. At the same time the Bulgarian army began to advance on Macedonia. There the local population, a proportion of which was openly sympathetic to Bulgarian aspirations, joined in the fighting on the side of the Bulgarians. Although the Bulgarian army attempted to drive the entente forces from southern Macedonia, it met with failure. This defeat was followed by a period of prolonged trench warfare on the Balkan front. By 1916 Bulgaria was also at war with Romania and, with the help of German and Austrian units, managed a victory over the Romanians.
While the war dragged on, the internal political situation was rapidly deteriorating. The country was in a state of economic chaos, and the living conditions of laborers and peasants continued to decline. Farm production dropped quickly, resulting in famine and soaring prices. These dire conditions gave a strong impetus to the growing antiwar movement in the country. The movement was headed by the left-wing Socialists, who attempted to correlate the antiwar movement with socialist propaganda. The Russian Revolution of 1917 stirred some elements of the Bulgarian population who, like the Russian people, felt that their government failed to represent their interests and was unresponsive to their needs. There were open revolts in the towns and villages; underground activities were growing within the Bulgarian army itself.
By 1918 Bulgaria and the Central Powers were defeated, leaving Bulgaria in a worse position than before the war. Hopes of regaining Thrace and Macedonia were dashed, and the country was immeasurably weakened by external fighting and internal division. The people were frustrated and bitter. Although the war had stimulated Bulgaria's industry—there were 345 industrial enterprises in 1911 and 1,404 in 1924—it had been costly in other respects. Bulgaria was forced to pay both reparations and payments for the allied occupation that followed. Taxes rose, and the value of the currency declined. As a result, King Ferdinand was forced to abdicate in 1918, shortly before the armistice was signed.
The Treaty of Neuilly-sur-Seine was signed on November 27, 1919, ending Bulgaria's role in the war and establishing her boundaries. Once more Bulgaria had entered a war on the losing side, and once more its irredentist ambitions had resulted in no territorial gains. At the end of the war Bulgaria lost Thrace to Greece—thus failing in her attempts to gain access to the sea—and a small area in the Rodopi (or Rhodope Mountains) and a portion of its western frontier to Yugoslavia. As a result of these losses, Bulgaria was left with a still greater sense of frustration and hostility toward its Balkan neighbors.