Ten years of almost continuous war began with the onset of the Balkan Wars in October 1912 and lasted—at least for Serbia—through World War I and to the resolution of the status of Albania in May 1922. This decade was decisive both in shaping the modern Serbian state and in connecting Serb national consciousness to a Yugoslav state that would include all Serbs.

Despite their competing expectations of territorial expansion in the area, Serbia, Bulgaria, Montenegro, and Greece concluded in 1912 a series of secret treaties creating a Balkan League, the explicit intention of which was to eject the Turks from Europe. On October 8, 1912, Montenegro declared war on the Ottoman Empire, precipitating the First Balkan War. The Serbian army pushed into northern Macedonia (Vardar Macedonia), and the Bulgarian army reached the gates of Constantinople in a matter of weeks. Bulgaria’s refusal to accept the division of Macedonia instigated a brief Second Balkan War in 1913, the result of which was Serbia’s division of the Sandžak with Montenegro and acquisition of Kosovo and Metohija, as well as the lion’s share of Macedonia. Its area was expanded by some four-fifths and its population by more than half.

The outbreak of World War I

The situation was unstable, however, for on Austrian insistence Serbia and Montenegro were forced to yield part of the territory they had occupied to form a newly independent Albanian state. Because Greece obtained Salonika (Thessaloníki), Kavála, and coastal Macedonia (Aegean Macedonia), the Serbs were denied a direct outlet to the sea that they had desired. The Austrians, meanwhile, saw in the emergence of a strong Serbia an end to their own Drang nach Osten (“drive to the east”). The rivalry between the two states reached a peak on June 28, 1914, when the Austrian archduke Franz Ferdinand attended a military review in Sarajevo—a heavy-handed, if unintended, provocation on Vidovdan, Serbia’s national day. He and his wife were assassinated by adherents of the secret society Mlada Bosna (“Young Bosnia”), who were armed by Crna Ruka. The Austrian authorities issued an ultimatum intended to be unacceptable, including a demand that Austrian officials be allowed to conduct in Belgrade an investigation into the assassination. The Serbian reply, though conciliatory, refused acceptance of that condition, and in July the two countries went to war. Germany joined the Austrian side a short time later as the conflict expanded to become World War I.

The Austrian offensive of August 1914 was forced back, as was a second attack in November. In the winter of 1914–15, however, a terrible epidemic of typhus struck Serbia, devastating both the civilian population and the army. When the German general August von Mackensen opened a third offensive with the assistance of the Bulgarians in October 1915, the weakened Serbs were unable to sustain a defense on two fronts and were forced to retreat across Albania to the Adriatic coast. Devastated more by the ravages of winter in the mountains than by Albanian attacks, the remnants of the Serbian army were transferred by French ships to the safety of Corfu, a Greek island in the Ionian Sea.

The rise to power of the Greek prime minister Eleuthérios Venizélos in November 1916 brought Greece into the war on the side of the Triple Entente. It became possible to open a new front against the Bulgarian-German forces in Macedonia, with the Serbian army playing a key part alongside British, French, and Greek units. After two weeks of hard fighting in September 1918, the Bulgarian line broke. The collapse of the Macedonian front was one of the most important factors precipitating the end for the Central Powers and the end of World War I. After Belgrade was recaptured on November 1, 1918, the forces of Austria-Hungary agreed to an armistice.

The Corfu Declaration

Following its evacuation in 1915, the Serbian government had worked from exile on Corfu for the reconstitution of its state. During the early part of the war, a number of prominent political figures from the South Slav lands under the Dual Monarchy had fled to London, where they had set up a “Yugoslav Committee.” Aided by sympathetic British intellectuals, the committee had worked to improve the position of South Slavs within the Monarchy in any postwar settlement. One of the most important achievements of the committee was its discovery of the Treaty of London—a secret document drawn up in April 1915 by which the Italians were promised Istria and large areas of Slovenia and Dalmatia in return for their participation on the Entente side. The stagnation of the war during 1916 and early 1917 added to the general indifference of the major Entente powers to the fate of the Slavic minorities within Austria-Hungary, and, thus, the Yugoslav Committee and the Serbian government-in-exile decided to seek a common program. In July 1917 representatives of the two groups met in Corfu and signed the Corfu Declaration, which called for a single democratic South Slav state to be governed by a constitutional monarchy. At the same time, on Habsburg territory, Croatian and Slovene deputies to the diets in Vienna and Budapest began preparing the ground for independence through a National Council.

The Corfu Declaration required that both parties to the agreement reorient their war aims. Serbs from the Habsburg lands had previously aspired to greater autonomy for Slavs within the empire. The Kingdom of Serbia, meanwhile, had seen the war as a defense of its gains of 1913—and even as a possibility that these gains might be extended. Indeed, the Serbian leader Nikola Pašić regarded the new alliance with dismay, as he saw Serbia’s freedom potentially compromised within a new political unit in which Serbs could be outnumbered by other constituent nations. Nonetheless, as it became apparent in 1918 that the Italians were not content with the territories allocated to them by the 1915 Treaty of London, the “Yugoslavs” sought the effective support of the advancing Serbian army. All sides were constrained by the major Entente powers to reach an accommodation, and a conference held in Geneva in November 1918 concluded with a declaration of union by representatives of the Yugoslav Committee; the National Council of Slovenes, Croats, and Serbs; and the Serb political parties. The Montenegrins had risen against Austrian occupation in September, and on November 26 a national assembly in Podgorica declared for union with Serbia under the Karadjordjević dynasty. In October the Sabor in Zagreb had declared the union with Hungary to be severed, and on December 1, 1918, a delegation from the National Council invited the prince regent Alexander to proclaim the new union. Four days later the Kingdom of Serbs, Croats, and Slovenes was announced to the world.