Creation of Yugoslavia

In 1916 the Serbian Parliament in exile decided in favor of the creation of the Kingdom of Yugoslavia at a meeting inside the Municipal Theatre of Corfu.[2] During June and July 1917, the Yugoslav Committee met with the Serbian government in Corfu and, on 20 July, a declaration that laid the foundation for the post-war state was issued. The preamble stated that the Serbs, Croats and Slovenes were "the same by blood, by language, by the feelings of their unity, by the continuity and integrity of the territory which they inhabit undividedly, and by the common vital interests of their national survival and manifold development of their moral and material life." The future state was to be called the Kingdom of Serbs, Croats and Slovenes and was to be a constitutional monarchy under the Karađorđević dynasty.[3]

After the collapse of Austria-Hungary, Syrmia became part of the newly formed State of Slovenes, Croats and Serbs. On 29 October 1918 the Parliament of the Kingdom of Croatia-Slavonia (an autonomous kingdom within the Austro-Hungarian Empire) severed ties with Vienna and Budapest. On 5 November 1918 the town of Zemun invited the Serbian Royal Army to protect the city from the withdrawing forces of the Central Powers. On 24 November 1918 as per the decision of self-determination, local parliamentary deputies from the Serb-inhabited parts of Syrmia which historically corresponded to the Serbian Voivodship constituted a National Council in Ruma. Members from the western part of the county, mainly inhabited by ethnic Croats (Šokadija region), did not have representatives in this assembly. The National Council, fearing that unification would not be achieved and concerned that the leadership in Zagreb was facing numerous difficulties and was slow to act, decided to join in the creation of a common state of Serbs, Croats and Slovenes. The Council decided in addition that, in the event that such a project of unification went unrealized, it would join the state as a part of the Serbian people's land.

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  Syrmia as part of Serbian Vojvodina (1848–1849)
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  County of Syrmia (1882–1918)

With the defeat of the Central Powers and the impending crumbling of the Austro-Hungarian Dual Monarchy, the monarchy collapsed and various regions were taken over by local self-styled National Councils beginning in the summer of 1918. Serb and other Slavic representatives founded the "Serb National Committee" in Novi Sad, which soon formed branches all across Banat, Bačka and Baranja in order to create a provisional administration. It particularly aimed at including other Slavs, most notably the Bunjevci. The Committee drafted a para-military militia, known as the "Serb National Guard", to secure its interests. Fearing that the troops would be too weak to face the Central powers, on 5 October 1918 the Pančevo local administration sent a plea to Belgrade for the protection of the Serbian Royal Army.

In Temeschwar on 1 November 1918 the local Social Democratic Party proclaimed a Banat Republic with the intention of preserving the Banat as a multi-ethnic region against Serbian and Romanian claims. The Republic was not able to achieve control over most of the territory it claimed, and, because the Belgrade Agreement of 15 November 1918 and previous Allied mandates to Serbia had mandated it to be taken over, the Serbian Army entered western and central parts of Banat (including Temeschwar) and abolished the republic; the Romanian army entered the eastern part of the region. Bačka and Baranja were also handed over to provisional local Serbian administration that governed from Novi Sad: after welcoming the Serbian Army, the Serb National Committee proceeded to finish taking over the administration from Hungarian authorities. The committee had previously formed rules to elect a National Council, which would decide about the self-determination of the majority people of the region, the Serbs (Slavs), as per the agreement with the provisional Hungarian government (which had broken off relations with Austria about a month before). All ethnic Slavs over the age of 20 had the right to vote. Democratic in spirit, the election introduced women's suffrage.

On 25 November 1918 the "Great People's Assembly of Serbs, Bunjevci and other Slavs from Banat, Bačka and Baranja", with 757 representatives elected in 211 municipalities, was constituted. 578 representatives were Serbs, 84 Bunjevci, 62 Slovaks, 21 Rusyns, 6 Germans, 3 Šokci, 2 Croats and 1 was Magyar. Two currents were opposed at the parliament, the Democratic and the Radical option. The weaker Democratic side wanted close ties to the State of Slovenes, Croats and Serbs, and as a compact part of the former South Slavic area of Austria-Hungary, they wanted to enter negotiations with the Kingdom of Serbia; they emphasized the unity of the Yugoslavian people and rejected inner divisions among national groups. The Radicals under Jaša Tomić, on the other hand, argued that the three peoples had different cultural, religious and historical backgrounds and that, although a Yugoslavian state was inevitable, these peoples could not be treated as a single ethnic group, and thus that an immediate unconditional union with the Kingdom of Serbia was needed first to mark out an ethnic Serbian territory. In the end the Radical option won because of the fear that if union with Serbia was not realized immediately, Vojvodina might find itself outside of Serbia in the end. The parliament decided as well that the territories created under the ceasefire were permanent, and that they were to be merged into the Kingdom of Serbia. It proclaimed itself the provisional legislative body for the regions and elected a provisional executive body, the People's Administration for Banat, Bačka and Baranja, under Dr. Jovan Lalošević. Although government in Belgrade accepted the decision of unification of this region with Serbia, it never officially recognized newly formed provincial administration.

After the Kingdom of Serbs, Croats and Slovenes was proclaimed, the National Council elected its share of members of the Provisional National Representorship of Serbs, Croats and Slovenes. Baranja became a hideout for communist and other refugees from Miklós Horthy's White Terror. The Treaty of Trianon had assigned most of the Baranja region to Hungary, which led to massive protest and a group of people under painter Petar Dobrović to proclaim a Serb-Hungarian Baranya-Baja Republic. This Republic lasted only a few days, and on 25 August 1921 it was invaded and annexed by Hungary, in accordance with Hungarian borders defined by the Treaty of Trianon. The Treaty of Trianon assigned to Hungary some of the most northern territories under Serbian control, in which a minority of South Slavs remained. On the other hand, sizable German and Magyar minorities were left within the Kingdom's borders. Central Banat was granted to Romania, as the region was divided on ethnic grounds, so as to contain a majority of the populations, leaving a minority of Yugoslavs in Romania and a minority of Romanians in the Kingdom of SCS. The BBB region remained a historical entity in the united realm until 1922 when a new administration was adopted in accordance to the unitary system. The region was split among the Bačka (with center in Novi Sad), Belgrade and Podunavlje (with center in Smederevo) administrative areas. When the Kingdom of Yugoslavia was proclaimed in 1929, most of the region eventually became a part of the Danubian Banate, with a small part going to the City of Belgrade.

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  Banat Republic (1918)
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  Region of Banat, Bačka and Baranja that proclaimed unification with Serbia
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  parts of Banat, Bačka and Baranja recognized as a territory of the Kingdom of Serbs, Croats and Slovenes at a 1919–1920 Paris Peace Conference

Montenegro was originally created by the national-romantic desire of liberation the lands which belonged to the State of Zeta, later of unification of South Slavic lands, and remained conservative in its ideology as compared with the other parts of the future Yugoslavia. In 1848 Prince-Bishop Petar II Petrović-Njegoš accepted the Zagreb-inspired proposal of the Serbian government to create a common state of all southern Slavs known as "Yugoslavia" and cooperated on the matter, but requested first a unification of the Serbs unification and later one with Bulgarians and Croats. In 1907 parliamentarism was born in Montenegro, and the first political party, the People's Party, expressed the need to cooperate and bond with other Slavic peoples, along with Serbian national unification and liberation. Entering gradually into periods of cold relations with Serbia and disappointed that he and his country had lost the primate in the Serb revolution, HRH Nicholas I of Montenegro accepted union with Serbia and in 1914 initiated the process, which was however interrupted by World War I; he also accepted the idea of a Yugoslavian realm.

Kingdom of Montenegro (1910–1918)

Shortly after entering the war on the side of Serbia to support escape of Serbian army toward Greece, the Kingdom of Montenegro was occupied by Austro-Hungarian military forces in early 1916. During exile Serbia and all other Allied powers recognised the King's government-in-exile as the government of Montenegro. In the spring of 1916 the King proclaimed Andrija Radović as prime minister, but he resigned a few months after his proposal of union with Serbia was rejected. He created in 1917 the National Committee for Unification with Serbia, which found support from Nikola Pašić's Serbian Government. In 1918 the Allies took control of Montenegro and mandated a common mission for its occupation. On 15 October 1918 the Government of Serbia named a "Central Executive Committee for Unification of Serbia and Montenegro" that would organize the process of unification. Ten days later the Committee decided to schedule a nationwide election with new election laws.

With this decision against the Montenegrin constitution, the committee created by Serbia had abolished the Montenegrin parliament and reversed the order of the King for a session of the parliament on first day after an armistice was signed.[6] The official reason for this decision was that 2/5 of the parliament members were abroad, making it necessary to elect new ones.[6] An election was held without a list of eligible voters,[7] and the vote was reportedly controlled by officials from Serbia.[6] The Podgorica Assembly (formally the Great National Assembly of the Serb People in Montenegro) elected in that way and encircled by detachments of the Serbian army[8] decided on 26 November 1918 to dethrone the King and the House of Petrovic-Njegos in favor of the House of Karadjordjevic and to unite with Serbia, pending a common state of Serbs, Croats and Slovenes.

The Podgorica Assembly elected a provisional executive body known as the "Montenegrin Committee for Unity with Serbia" under Marko Daković which oversaw Montenegro's integration, until the SCS's government took over on 23 April 1919. The Assembly also elected its share of representatives into the Provisional National Representorship of the Kingdom of Serbs, Croats and Slovenes.

Reaction to these events escalated in early 1919 into the Christmas Uprising by opponents of annexation. International leaders opposed the uprising and the Serbian forces violently quelled the rebellion.[9]

Bulgaria fought on the side of the Central Powers during World War I which lost the war. Initially, the Allies had attempted to persuade the country to join the Allies by having Serbia cede large parts of Macedonia to Bulgaria in exchange for gaining Bosnia-Herzegovina and an outlet to the sea in the Treaty of London in 1915. The Serbian government was unwilling to officially confirm this offer and Bulgaria eventually joined the Central Powers. However, by the end of the war, many Bulgarian politicians became interested in joining the newly formed Yugoslav state alongside extant Bulgarian supporters of a united South Slavic state such as Aleksandar Stamboliyski. Their reasons included to avoid paying war reparations for having fought the Allies, and to unite with their ethnic brethren in Macedonia. One initial plan considered by the Serbian leadership was to accept the Treaty of London 1915 in which Serbia gained Bosnia-Herzegovina, Slavonia, and Southern Dalmatia and cede Macedonia to Bulgaria, and then constitute a Yugoslav state between Serbia and Bulgaria. Under this proposal, the largely Croat and Slovene areas would remain part of the Austro-Hungarian monarchy and would be liberated at a future date. This plan never materialized, partly because the Allies decided to scrap the Treaty of London in favor of self-determination and partly because the Austro-Hungarian Monarchy itself collapsed leaving all the South Slav areas free to join a Yugoslav state.