On 5 December 1918, four days after the proclamation of the Kingdom of Serbs, Croats and Slovenes, the National Guards (an armed force of the National Council of the State of Slovenes, Croats and Serbs) and Sokol volunteers suppressed a protest and engaged in an armed clash against the soldiers of the 25th Regiment of the Royal Croatian Home Guard and the 53rd Regiment of the former Austro-Hungarian Common Army. National Guardsmen stopped the soldiers at the Ban Jelačić Square in Zagreb.
Reasons for the protest and the conflict are not very well documented, but the soldiers who marched down Ilica Street from the Rudolf barracks towards the central city square shouted slogans against the King Peter I of Serbia and in support of republicanism and the Croatian People's Peasant Party leader Stjepan Radić. Once the soldiers reached the Ban Jelačić Square, brief negotiations took place, and then an armed clash afterwards. Most of the eighteen people killed in the clash were soldiers, and the dead protesters were dubbed December Victims (). Perceiving them unreliable, the National Council first disbanded the two regiments and later all former Austro-Hungarian units based in the new state. The National Council then relied on the Royal Serbian Army to establish units to replace the recently disbanded ones.
The Frankist faction of the Party of Rights used the event to portray creation of a common South Slavic kingdom and other events of 1918 as national humiliation claiming it fostered "culture of defeat" among Croats. The Frankists claimed that the "culture of defeat" was the result of a series of political failures and that the Frankists would give the disenchanted people and ignored former Austro-Hungarian officers a chance to redeem themselves for their defeats. Thus the "culture of defeat" contributed to the rise of Ustaše as far-right paramilitaries and later Nazi collaborators during the World War II occupation of Yugoslavia.
Background Collapse of Austria-Hungary and civil disorder
In the final days of the World War I, on 5–6 October 1918, political parties representing Croats, Slovenes, and Serbs living in Austria-Hungary organised the Zagreb-based National Council of Slovenes, Croats and Serbs to achieve independence from the empire. The National Council proclaimed the State of Slovenes, Croats and Serbs encompassing the Slovene Lands, Croatia-Slavonia, Dalmatia, and Bosnia and Herzegovina, and authorised the Yugoslav Committee, an interest group advocating unification of previously Habsburg South Slavic areas with the Kingdom of Serbia, to represent the council abroad. National Council president Anton Korošec left Zagreb for a conference in Geneva with Serbian representatives to discuss the method of unification.
At the time, Austro–Hungarian deserters termed Green Cadres were causing a crime wave in the countryside. By September 1918, there were about 50,000 Green Cadres among the Croats, Serbs, and Bosniaks. Most of them were active in Croatia-Slavonia, where violence peaked between 24 October and 4 November. The period also saw a mutiny in Požega. In nearby Orahovica, two Austro-Hungarian regiments, one Bohemian and one Dalmatian fought against each other. Officials in the town reported that some of the soldiers sided with the Bolsheviks. The violence quickly spread and elements of the 23rd Regiment and the 28th Regiment of the Royal Croatian Home Guard joined in looting Osijek. Mutineers also led looting in Petrovaradin, Pakrac, Daruvar, and Županja, although peasants and the (mostly peasant) Green Cadres were responsible for most of the pillaging and looting.
The National Council hesitated to condemn the violence, and its attempts to stop the looters by deploying ad-hoc, locally raised militia were ineffective since many militiamen were also looting. Therefore, the National Council relied on Serbian prisoners of war (captured by the Austro-Hungarian Army during the war), and sent a delegation to the Royal Serbian Army command on 5 November to request its troops to restore order in Croatia-Slavonia. The National Council, by then dominated by the Croat-Serb Coalition led by Svetozar Pribičević, blamed the unrest partly on Bolsheviks and the Croatian People's Peasant Party (HPSS) led by Stjepan Radić. The association of the HPSS with the popular discontent later helped propel the HPSS to the position of the most successful political party among the Croats in the interwar period. The peasants actively involved in the October–November unrest, misidentifying republicanism as the abolition of military service and taxes, cited it as their ultimate political objective.
Federation vs centralised union with Serbia
There were two main approaches to the unification of the South Slavs. While Ante Trumbić's Yugoslav Committee advocated a federal system of government, the Prime Minister of Serbia Nikola Pašić wanted a centralised state. Pašić threatened to conquer and annex the Serb-inhabited territories of Austria-Hungary to create a Greater Serbia unless Trumbić accepted a centralised state. Under pressure from the Triple Entente, Pašić agreed to support a federal South Slavic state during the November 1918 conference in Geneva, but Serbia repudiated the agreement either because of Prince Regent Alexander's opposition, or in a scheme devised by Pašić to deflect Entente pressure and undermine Korošec's authority.
Shortly after the conclusion of the Geneva conference, the National Council announced it had thwarted an attempted coup d'état for which it arrested General of the Infantry Anton Lipošćak. The Italian Army seized Rijeka and approached Ljubljana. Without means to stop the Italian advance, the National Council feared that the Italian presence on the eastern shores of the Adriatic would become permanent. The National Council dispatched a delegation to Prince Regent Alexander to quickly arrange unification of Yugoslavia on a federal basis. The delegation ignored the National Council's instructions to demand constitutional safeguards when it addressed the Prince Regent on 1 December. The Prince Regent accepted the unification offer on behalf of Peter I of Serbia, and the Kingdom of Serbs, Croats and Slovenes was established without any agreement on the nature of the union.
Armed forces in Zagreb
The National Council established the National Guard on 27 October 1918 in preparation for the Croatian Sabor meeting that declared secession from Austria-Hungary two days later. The National Guard consisted of volunteers from university guard organisations and Croatian and Serb Sokol associations, subordinated to the Commission for Public Order and Security in Zagreb headed by Budislav Grga Angjelinović and directly commanded by Lav Mazzura. The force was augmented by a detachment of former Austro-Hungarian Navy sailors. Attempts to organise the National Guards in the countryside to combat civil disorder proved ineffective.
The State of Slovenes, Croats and Serbs formally established its military on 1 November, three days after the declaration of independence, from Austro-Hungarian units based in the territory of the new state. On 6 November, the 25th Regiment of the Royal Croatian Home Guard and the 53rd Regiment of the Common Army based in Zagreb swore an oath of allegiance to the National Council. The council deemed the soldiers returning from the war after that date also bound by the same oath. The 25th Regiment had just returned from fighting in to capture Međimurje on behalf of the National Council, and both regiments maintained security in Zagreb without incident. Nonetheless, many soldiers based in Zagreb supported a republic; republican ideas spread under the influence of Radić and returnees from Russia in the aftermath of the October Revolution. In early December 1918, the 25th Regiment commanded by Colonel Milivoj Kućak had 210 officers and 578 soldiers stationed in Zagreb barracks of the Royal Home Guard in the Ilica Street, while the 53rd Regiment had 442 troops stationed in the city, in the Rudolf barracks. The 53rd Regiment, commanded by Colonel Mirko Petrović, the 37th Field Artillery Regiment of the former Common Army, and the 6th Field Artillery Regiment of the Home Guard were also stationed in the city. The 37th Field Artillery Regiment had 22 officers and 142 soldiers, while the 6th Field Artillery Regiment had 46 officers and 21 soldiers in Zagreb. The National Council-established National Guard had about 500 armed members in Zagreb at the time, augmented by a 1254-strong regiment composed of former Serbian Army prisoners-of-war. In November, Lieutenant Colonel Dušan Simović was assigned to Zagreb as the envoy of the Serbian Army, and the 3rd Battalion of the 7th Regiment of the Serbian Army arrived in Zagreb by the end of the month.
Prelude
On 3 December, the National Council promulgated the Unification Act. In cooperation with Zagreb's local authorities, it sponsored several public celebrations of unification to match the mass celebrations of declaration of independence of the State of Slovenes, Croats and Serbs from Austria-Hungary from late October. According to historian Rudolf Horvat, the festivities were organised carelessly and some behaviour offended "everything held dear and sacred by the Croatian people". The same day, there were reports from the nearby town of Bjelovar that the army troops stationed there were mutinous after the unification was announced. A National Council representative in the town reported that the soldiers were shouting slogans against the King and cheering on republicanism. Kućak and Petrović informed the deputy defence commissioner of the National Council Nikola Winterhalter of the pro-republican mood in the troops stationed in Zagreb barracks.
Seizing on widespread disenchantment, the Frankists drew up and distributed a proclamation condemning the process of unification as undemocratic on 2 December. The party daily Hrvatska (Croatia) published it two days later, stating the Frankists would continue to advocate unification of free and independent states of Slovenes, Croats, and Serbs in a federal republic. In response, the authorities confiscated the issue and banned Hrvatska. The party distributed the manifest as a leaflet instead. In the morning of 5 December, Zagreb Cathedral held a Te Deum service as a part of celebration of establishment of the Kingdom of Serbs, Croats and Slovenes.
Protest From the barracks to Ban Jelačić Square In the afternoon of 5 December, some soldiers of the 53rd Regiment left the Rudolf barracks in western Zagreb and set out towards Ban Jelačić Square. En route, they stopped before the Home Guard Barracks in Ilica Street where some soldiers of the 25th Regiment joined the march. Civilians also joined the soldiers. The soldiers brought rifles and two machine guns from each barracks and were accompanied by the twelve-strong military band of the 25th Regiment. The marchers intended to declare a free Croatian republic, spurred on by perceived provocative behaviour at celebrations of unification. The subsequent indictment for the act of mutiny specified 250 soldiers participating, but the actual number is likely to be about 400, 200 from each regiment.