Serbian Campaign
Central Powers invasion of Serbia
28 July 1914 - 3 November 1918
author Paul Boșcu, November 2016
The First World War started with the Austro-Hungarian invasion of Serbia. The Austrians, ill equipped and fighting in unknown territory suffered a humiliating defeat at the hand of the Serbs in the first months of the war. A year later, a combined German, Austrian and Bulgarian attack was launched and the weak Serbian army could not stand against such overwhelming odds. The Serbian army was evacuated to Greece, were they would take part in the Salonika campaign. Serbia itself was under occupation until the defeat of the Central Powers in 1918.
The Serbian Campaign in the Great War started when the Austro-Hungarian Empire attacked the Kingdom of Serbia. The invasion became a disaster for the Austro-Hungarians when the Serbian army turned out to be a tougher opponent than anticipated. As such, the Serbians managed to succesfully defend their homeland in 1914. In the following year however the Austrians, with German help, managed to defeat the Serbians who retreated their armies to Greece, through Albania, where they could reorganize under the protection of the other Entente combatants. Serbia was under Central Powers occupation until the end of the war in 1918.

Serbia's geographical position made it the strategic keystone of the Balkan peninsula. The terrain was wild and mountainous but two historic Balkan trade routes passed through it along the Morava-Maritza Trench, known as the 'Diagonal Furrow' (the line selected for the Berlin-Baghdad railway), and the Morava-Vardar Trench, connecting Central Europe with the Aegean. Serbia's northern frontier was shielded by natural barriers: the rivers Drina and Danube. A third barrier, the river Sava, was lined with near-impassable marshes. Road communication throughout the country was extremely poor.

Austria's principal emotional, if not rational, war aim was the punishment of Serbia, which had precipitated the July crisis by its involvement in the Sarajevo assassinations. Sense would have argued that Austria should deploy its whole strength forward of the Carpathians to engage the Russians. Outrage, combined with decades of provocation, demanded the defeat of the Belgrade government and the upstart Karadjordjevic dynasty.

The Serbian officer corps' participation in the murder and mutilation of the Obrenovic King and Queen in 1903, and the widely reported practice of mutilation of corpses during the Balkan Wars had led the Austrian army to imagine that a campaign in the Balkans would present little more difficulty than the British or French commonly encountered in their colonial campaigns in Africa or Asia. The Austrians expected a walkover. In fact the Serbs, despite their cruelty during the Balkan Wars, were not at all militarily backwards in tactics.

The political pressure for an early attack on Serbia was considerable. Domestically, victory would quash irredentism; diplomatically, it would provide the foundations for a Balkan alliance. Strategically, pure defense against Serbia was not recommended, since it would involve inferior forces stretched along a frontier totalling 600 kilometres, with lateral communications so poor that rapid concentration would be impossible.

The Austro-Hungarian campaign against Serbia in 1914 failed to meet any of the required political objectives of 1914. Vienna could not 'halt at Belgrade' as the Kaiser requested because it had no plan for such an operation; nor could the army deliver the quick victory the diplomats wanted in order to shore up the empire's position in the Balkans.

The approximately 200,000-strong Serbian Army was commanded by the elderly figure of Field Marshal Radomir Putnik. He would prove a formidable directing intelligence to Serbian military operations. The Serbian Army had recent experience in the Balkan Wars, but it was woefully ill-equipped for a full scale conflict with a major power.

Putnik had to endure the embarrassment of being promptly imprisoned by the Austrians in Budapest, where he had been undergoing an untimely medical treatment when the war started. Strangely, he was then released, presumably because the Austrians thought he would hardly be fit to exercise a competent wartime command. However, his offer to resign on the grounds of ill health having been rejected by King Peter I of Serbia, Putnik went on to oversee the strategic direction of the Serbian Army, while his subordinates did all the work in the field.

The small Serbian First, Second and Third Armies faced the 270,000 men amassed in the Austrian Fifth and Sixth Armies with little immediate tactical ambitions other than to endure till their Russian allies had triumphed. The strength of the Serbian army lay in the endurance and courage of its officers and soldiers, who displayed amazing powers of survival in their campaigns.

The Serbian military system demanded universal service for all able-bodied males from the age of 18 to 45. The system of conscription mobilized, even if by informal means, a higher proportion of the male population than in any other European country. The army conspicuously lacked motorized transport, due in part to the appalling standard of Serbian roads, generally impassable to motors after rain. The army's transportation relied on animals. Baggage trains, bridging equipment and artillery were all drawn by oxen.

The Balkan wars had also weakened the Serb army. The newly acquired territories had not been fully assimilated for military purposes, and parts were in near revolt. Total losses may have risen as high as 91,000. More serious for a country of economic backwardness was the loss of equipment and the expenditure of ammunition. On 31 May 1914 the minister of war, having embarked on a ten-year program to rebuild the army, declared that Serbia was not yet fit to fight.

The rifles in use were of a variety of types (ironically, the best and most widely used, Mausers, had been supplied by Germany), and there were only enough modern patterns for the peacetime complement of 180,000. In some units up to 30 percent of infantrymen had no rifles at all. There was less than one machine gun for each infantry battalion. The Serbs had acquired 272 75 mm field guns from the French, and had better field howitzers than the Austrians. But after they had given 100 guns to Montenegro, their total complement of field guns was 528, of which only 381 were quickfirers. The recent fighting had depleted shell stocks.

The Serbs' reliance on the Entente powers for equipment created a dependence that robbed them of strategic freedom, and a vulnerability which their land-locked isolation did nothing to mitigate. The Russians sent 150,000 rifles, the French sent artillery; in exchange, both powers demanded that the Serbs attack.

Putnik, the son of a teacher, a gunner and former lecturer at the military academy, had stood at the apex of the Serbian army since 1903, as Chief of the General Staff for most of the time, and minister of war for the rest. He was 67 and suffered from emphysema, but he had two great strengths: he commanded the respect of the competing political groups in Serbia, and he was thoroughly familiar with the plans for his country's defense.

Putnik's return from taking the waters at Gleichenberg was followed by a bout of pneumonia. He did not, therefore, arrive at his headquarters until 5 August. Extraordinarily, he had taken with him the keys to the safe in which Serbia's war plans were locked. His staff had to blow it open before they could begin the process of mobilization and concentration. Putnik had an able deputy, Zivojin Misic.

Putnik's preferred modus operandi was offensive defense: he deployed defensively and in depth, but only as a preliminary to the counterattack. He reckoned that, on balance, the Austrians would attack from the north. However, he concentrated his three armies in such a way that they could, if necessary, face a threat from the west.

The Austrian army was strong on tradition, with many of its regiments claiming descent from those that had fought the Turks in the 17th century. With the steady expansion of the empire, however, it had been necessary to recruit increasingly from non-German elements. Problems of loyalty and language arose as German-speaking units became outnumbered by the other ethnic groups.

By 1914 less than 30 percent of the army was Germanic. Germans, Hungarians and Czechs, being the better educated, went into the artillery, engineers and cavalry. Almost 70 percent of the men in the so-called Common Infantry regiments were Slavs. Magyars disliked Slavs, and care had to be taken in mixing their formations. Language was a major problem, tackled by using a universal patois known as 'Army Slav' in addition to which recruits were required to learn up to 80 German words of command.

The General Staff tinkered with the deployment of three groups: the ‘A-Staffel’ that would go to Galicia in the event of a Russian war, the ‘Balkan Group’ that would attack Serbia, and the ‘B-Staffel’ that would participate in either campaign, depending on the promptness of Russian mobilization. The railway planning section prepared timetables accordingly.

Conrad von Hötzendorf, the Austro-Hungarian Chief of Staff, was discovering that despite his haste to go to war, the army was ill-prepared for active service. He also had to deploy eight army corps to the Russian border. He had long since prepared a plan to deal with Serbia alone, a situation known as ‘War Case B’. During 1912-13, however, increasing consideration was given to the likelihood that a crisis with Serbia would precipitate a Russian war, ‘War Case R’, demanding that the Balkan army be reduced so as to strengthen the one in Galicia.

Austria-Hungary, like Germany, had no properly developed machinery for the coordination of the political and military direction of the war. As in Germany, this was the task of the emperor. Supreme command was a royal prerogative. Archduke Friedrich was appointed Commander-in-Chief for the operations in the Balkans. Friedrich was chosen because he would let Conrad have his head, but would complement the Chief of the General Staff by moderating his more impulsive side and conveying royal gravitas in dealings with Germany.

Despite the army’s shortcomings, Austria declared war on Serbia. A day later, Austrian warships on the Danube bombarded Belgrade as their 2nd, 4th and 6th armies under General Oskar Potiorek prepared to cross the rivers Sava and Drina. The Serbs, with 450,000 men supported by partly trained Montenegrins, all under command of Marshal Radomir Putnik, resolved to sell their lives dearly.

Putnik, with some 450 miles of frontier with Austria and Bulgaria to defend, deployed his three armies centrally to meet threats from either direction. He aimed to hold the key river lines with small formations, and then, having located the main crossings, to attack them in strength on ground of his own choice. He correctly forecast the Austrians' main thrust lines and was ready when they came.

When the rest of the army was mobilized, Archduke Friedrich became Commander-in-Chief of the Austrian armed forces as a whole. With the elevation of Galicia over Serbia, Przemyśl was chosen as his headquarters, and it now became necessary to appoint a separate theater commander for the Balkans. Oskar Potiorek, the military governor of Bosnia, had been named commander of the 6th army. He was also entrusted with responsibility for the Serbian front as a whole.

Potiorek had been passed over for the post of Chief of the General Staff in Conrad's favour. Thus, the most important difference between them was professional jealousy. Its symbol was the control and use of the 2nd army on Serbia's northern frontier: at an operational level its command was Potiorek's responsibility; at a strategic level its deployment was Conrad's. Not until his formal appointment did Potiorek know he was not to have full use of the 2nd army. It was a decision he never accepted.

Potiorek began to agitate for a measure of relative independence in relation to the army's supreme command, Armee Oberkommando (AOK). He was formally placed under the direct authority of the emperor. Thus, Conrad lost control of the conduct of operations in the Balkans after late August. Conrad's defenders have projected back from this to argue that the Chief of the General Staff's better judgement was thwarted by Potiorek from the outset. In reality the position was even worse: two opposite minds, not one, were shaping operations against Serbia.

Under orders from Conrad, the Austrian Fifth Army crossed the Drina River border. The Austrians were determined to finish the matter quickly and saw no problem in defeating their weak opponents. In doing so they not only attacked with only half their available strength, but worse still they were advancing into the rough country of western Serbia rather than the northern plains. Putnik was initially taken aback by the attack, imagining it to be a feint, but recovered swiftly to rush in reinforcements. The resulting four-day battle forced the Austrians to fall back.

Putnik expected an attack from the north out of Hungary across the Danube towards Belgrade. Instead, Conrad's plan was for an attack from the west, out of Bosnia, into the salient of Serbian territory enclosed by the Drina and Sava rivers. There was sense in it, for the salient is one of the few areas of level terrain in the whole of the country. At first the advance went well, benefiting from the Austrians' ability to attack concentrically, south across the Sava, east across the Drina. Had Putnik hurried his troops forward, they might have been encircled and trapped.

Putnik organized his main line of resistance behind the plain, along the River Vardar and the high ground beyond. The defenders brought devastating fire to bear on the attackers at close range. Potiorek signalled Conrad to request the intervention of the 2nd Army in order to take pressure off. Conrad granted his request, on condition that the ‘swing’ formation's departure for Galicia was not delayed. The Serbians, driven back and forward by the weight of Austrian artillery fire, always returned to the attack and gradually overbore the Austrians by their persistence.

Potiorek's approach was hesitant and many of his ill-trained troops were unwilling to fight fellow Slavs. There was much indiscipline in the ranks, and horrific atrocities were committed by Austrian units against Serbian civilians. In nine days of ferocious fighting, the Serbs threw the Austrians back across their start lines.

Small-scale Serbian offensives incurring onto Austro-Hungarian territory were markedly less successful, so the next major act occurred when the Austrians launched a twin-pronged attack by the Fifth and Sixth Armies across the Drina to secure a firm bridgehead. The fighting was murderous, as Putnik marshalled his smaller forces as best he could, launching counterattacks to disrupt the Austrian advance. The fighting climaxed in another four-day battle in the mountains, marked by a series of sanguinary frontal assaults by both sides. Eventually numbers told and the Serbs fell back, and trench warfare took its iron grip.

The Serbs followed up the initial victory they had won, and crossed into Austrian territory. It was an unwise maneuver and they lost nearly 5,000 casualties when forced to withdraw across the Sava. However, the Serbs found a weak spot in Potiorek's defenses on the Drina, crossed into Bosnia and raced toward Sarajevo. The Serbian occupation of eastern Bosnia lasted only forty days.

Heavy rain continued to hamper bridging operations, and once on the far bank both armies found their mountain guns outmoded when confronted with the Serbs' quick-firing field artillery. Potiorek's struggles to break out of the bridgeheads which had been established peaked in the mountainous areas south of Loznica: control of Jagodnja changed four times on the 22nd September alone.

Potiorek attributed his first defeat to the interventions of AOK and the loss of the 2nd army, rather than to his own failings. He began immediately to plan a second attack, and AOK, sensitive to the possibility of a Serb offensive, approved its commencement. At the Battle of Drina the Serbs had a crippling disadvantage: they had few guns and almost no ammunition, so the artillery exchanges were remarkably one-sided.

Potiorek had too few men to sustain operations simultaneously on the northern and western fronts. His complaints, that Conrad was starving him of troops and, above all, of munitions to feed the Galician front, at first found a sympathetic hearing. By October, however, Potiorek's refrain reflected the consequences of the positional warfare which now prevailed on the Drina front, as on others. Potiorek's operational solutions were not adapted to the new circumstances, or to the resources available to him, but continued to be derived from textbooks. In military, if not political circles, his efforts to undermine Conrad began to lose him face.

Whereas in August Potiorek had yet to secure his independence of AOK, by October he had, and the fact that he failed to deliver according to the grandiose expectations he generated reflected badly on him rather than on AOK. Caught in the crossfire between Potiorek and Conrad, Arthur von Bolfras, the chief of the emperor's military chancellery, became sufficiently frustrated by the end of September to consider installing Franz Joseph as Commander-in-Chief, with himself as Chief of Staff.

The Austrians attacked again, when they used their artillery superiority to push the Serbs back. The Serbs withdrew slowly at first but pulled right back to shorten their front. This meant that the capital, Belgrade, had to be abandoned, which the Austrians duly entered. Putnik launched a counterattack crashing first into the Austrian Sixth Army. The results were spectacular: the Sixth Army broke and fell back in complete disorder. At this point Putnik turned his forces to the Fifth Army, which also crumbled under the pressure. Facing complete defeat, the Austrian armies retreated back to the borders. Belgrade was recaptured by the Serbs.

In the interim, supplies of artillery shells had arrived for the Serbs, dispatched from the British and the French. This slightly rebalanced the equation, especially as the insightful Putnik divined that the Austrians were becoming overstretched as they pushed deep into Serbia.

By early November it seemed that all was up, but at that point the frail and elderly King Peter I of Serbia, carrying a private soldier's rifle, entered the trenches with his sons, inspiring his troops with the words: ‘Heroes - you have taken two oaths: one to me, your King, and the other to your country, I am an old broken man on the edge of the grave and I release you from your oath to me. From your other oath no one can release you. If you feel you cannot go on, go to your homes, and I pledge my word that after the war, if we come out of it, nothing shall happen to you. But I and my sons stay here.’ Not a man left the line.

Sheer weight of numbers forced the Serbs to evacuate Belgrade but Putnik, having completed a withdrawal in good order to the southwest, turned and counterattacked on the line of the Kolubara river, King Peter still in the front line with his rifle and 50 rounds of ammunition. The Austrians again fled in confusion.

After the Austrian collapse, Serbian patrols were back in Belgrade where the King attended a solemn Te Deum in the cathedral. The third Austrian invasion had collapsed ignominiously with the loss of 41,000 prisoners and 133 guns. Potiorek was replaced by the Archduke Eugene.

The campaign had been a fiasco for the Austrians: nothing had been achieved, thousands of men had died and the Serbs still preened themselves across the border, acting as beacons for all the disaffected minorities within their domains. Austria-Hungary had the war with Serbia she had craved in July 1914: distracted by the menace of the Russian armies, she did not have the strength to win it. After the Austrian defeat, the Serbian front was quiet for almost a year.

Strategically, if not tactically, Serbia had won a major victory. Austria-Hungary's bid to use military might to reestablish its Balkan pre-eminence had been thwarted. And yet its need for prestige prevented the dual monarchy from simply abandoning operations on its southern front.

The Serbian front now went quiet as the Austrians endeavored to cope with the alarming situation on their Russian front. In response to Serbian appeals, Admiral Ernest Troubridge of the British Mediterranean fleet, eccentrically clad in the uniform of a Serbian general to confound German intelligence, arrived in Belgrade in February 1915 with a naval detachment for the city's defense.

Conrad advocated the adoption of a defensive position against Serbia. He reckoned that a victory against Russia in Galicia, not the conquest of Serbia, would settle the Balkan aspirations of the empire. Potiorek disagreed. The tug of war between the two for troops kept the Austrian forces on the Drina stronger than they needed to be for true defense, but still too weak for a major offensive. The same applied in Galicia. Thus, in neither theater was a decisive concentration achieved.

Before 1915 ended, there was one enemy that Erich von Falkenhayn, the German Chief of Staff, accepted could be dealt with permanently in the period of grace granted by the string of defeats suffered by Russia in 1915: Serbia. He allocated the German Eleventh Army to the task of joining with Conrad’s Austrian armies in an assault on Serbia under the overall command of August von Mackensen. They were also to be helped by a new ally: the Bulgarians, who had been greatly impressed by the triumph at the Battle of Gorlice-Tarnów and had begun serious negotiations with a view to joining the war on the side of the Central Powers.

Germany astutely played on the Bulgarian resentments stemming from the chastening treatment meted out to Bulgaria in the second stage of the Balkan War of 1912. The Germans offered them substantial territorial gains at the expense of Serbia or indeed any other Balkan countries that had the temerity to join the Entente. These diplomatic moves were coordinated to coincide with the Mackensen Offensive, timed to commence in early October 1915, with the express intention of knocking Serbia out of the war.

Meanwhile typhus was decimating the Serb army: by April 1915, 48,000 soldiers were in hospital. The summer of 1915 saw little more than skirmishing as the Serbs built up their strength for what they realized would be a hard winter. Germany was desperate to reopen the Berlin-Baghdad rail link and could not do so until Serbia was conquered.

Entente counter-diplomacy, even a last-ditch ultimatum from Russia, failed to have any impact: the Bulgarians under Tsar Ferdinand I were determined to join the Central Powers.

German forces joined the Austrians on the northern border and the Entente belatedly realized that they had lost a major diplomatic battle by not insisting that the Greeks fulfilled the treaty terms binding them to help Serbia. A French mission arrived at Salonika to assess its suitability as a base for the support of the Serbs. In an effort to involve the Greeks, Serbia offered them territory on the border. King Constantine I reluctantly gave permission for Entente troops to land at Salonika as his prime minister made a vain last-ditch appeal for the Bulgarians to suspend mobilization if the Greeks did likewise. It was too late; the die had been cast.

The Austro-German forces massing on the northern frontier were commanded by Field Marshal August von Mackensen, fresh from his crushing defeat of the Russians at Gorlice-Tarnów. Charged with the total defeat of the Serbs he headed a joint force including the newly mobilized Bulgarians.

The odds overwhelmingly disfavored the Serbs. Serbia's only hope of altering the balance lay in attracting Entente troops into the Balkans, via the Greek port of Salonika. In the hope that an Entente intervention might now allow them to defeat the Bulgarians in the south before the Germans and Austrians developed their attack in the north, the Serbs made a plea to the French and British to endorse the Salonika plan. The plan was put into action, with the Greek Prime Minister Eleftherios Venizelos’ support. It was now too late, however, to save Serbia. Nonetheless the Macedonian front of World War 1 had opened, with the Entente and Central Powers fighting for supremacy in the Balkans.

An inducement to undertake the Salonika project came from an unexpected direction. On the day Bulgaria mobilized, Venizelos advised the British and French governments that if they would send 150,000 troops to Salonika, he was confident of bringing his country into the war on their side. Venizelos, ‘the lion of Crete’, who had won the independence of his island from Turkey in 1905, would have been a large man in any country and absolutely dominated the politics of the small Greek kingdom.

Venizelos was the standard bearer of the ‘Great Idea’: the national reunion of the Greek speaking communities of the Aegean and its hinterland at Turkey's expense. He believed equally in the necessity of Entente support to achieve it and in the likelihood of their eventual victory. He therefore viewed the organization of aid to Serbia as both realistic and necessary. At his persuasion, Britain and France agreed to send troops to Salonika.

After Venizelos was dismissed, the Entente took matters into their own hands. Greece, as a neutral without the means to resist, was obliged to acquiesce in the arrival of a Franco-British (and later also Russian) expeditionary force. Its arrival came too late to assist the Serbs.

Venizelos, however, overestimated the strength of his position at home. King Constantine was not only the Kaiser's brother-in-law but believed his kingdom's interests would be best served by preserving its neutrality. He dismissed Venizelos from office. Venizelos would return to politics in October 1916, form a government at Salonika which Britain would recognize as legitimate and, after Constantine's abdication in June 1917, resume the premiership with popular support. In the autumn of 1915, however, none of that could be foreseen.

Mackensen launched his assault with a heavy bombardment pounding the Serbian positions all along the Sava and Danube Rivers. The German Eleventh Army and Austrian Third Army managed to establish significant bridgeheads and, once the integrity of the Serbian river lines was broken, their weight of numbers soon hurled the Serbians back and Belgrade fell again. Then, the Bulgarian First and Second Armies invaded Serbia from the east. The campaign that ensued was brutal.

A huge artillery bombardment began the offensive. On the following day Belgrade came under attack and the British naval gunners fought to the end as the capital fell after savage street fighting costing the Austrians 7,000 casualties.

Mackensen's plan, after gaining his lodgement, was to envelop the Serbs by driving them southward into the center of their country. As agreed a month earlier, the Bulgarians crossed the frontier from the east, simultaneously sending troops south to oppose the British and French in Macedonia, while the Germans and Austrians pressed down from the north. Hard as the Germans and Austrians pressed their pursuit after the fall of Belgrade, they found it impossible to corner the Serbs against any obstacle.

The balance had tipped in favor of the Central Powers, and the great fortress of Mitrovitza fell to the Austrians as the Serbs withdrew south and west. On the same day the Bulgarians linked hands with General Max von Gallwitz's German troops. The Bulgarian advance had cut the Serbs off from the Anglo-French force now established in its bridgehead around Salonika, from which it had earlier been possible to supply Putnik's army.

The Serb retirement continued. Morale was still high, but they were steadily forced to give ground and the great arsenal of Kragujevac was abandoned and blown up. The army retreated onto the Kosovo Plain as the new seat of government was set up at Mitrovica. As winter closed in, the city of Monastir fell; the army was now in dire straits, its last links with Greece cut, typhus raging, all troops on half rations and only 200 field guns left. As Mitrovica and Pristina fell, the surviving 200,000 Serbian troops faced a hard march over mountains in the grip of winter, to safety on the Adriatic coast.

The Central Powers had underestimated both the sheer bloody-mindedness of the Serbs and the impact of the winter weather in the mountainous areas of the central Balkans. With their leader, Field Marshal Radomir Putnik, travelling in a sedan car, the Serbians eluded attempts to cut them off and fell back through the mountain passes into Montenegro and Albania. They then managed to reach the Adriatic where they were evacuated by the British to Greece. The Central Powers had captured Serbia, but the Serbian Army would fight on regardless.

The Serbian rearguard was overwhelmed on the White Drin river, losing masses of precious supplies in the process as the retreat went on in dreadful weather. A new seat of government and General Headquarters were established at Scutari on the Albanian coast as the Entente rushed shipping into the Adriatic to embark the battered survivors.

The Greek King was informed that the surviving Serbs were going to the island of Corfu, already occupied by French marines without the Greeks' permission; the transfer began in January 1916 as the Salonika garrison blew the bridge over the River Struma in the presence of indignant Greek troops. The Salonika campaign had got underway.

A French force that had belatedly set out from Salonika up the Vardar valley to help the Serbs was met by overwhelming Bulgarian forces and compelled to fall back in some disorder with a British division shielding its left flank. The Entente withdrew to a defended line, the so-called 'Entrenched Camp', some 14 miles inland from Salonika itself. There they remained for the rest of the winter.

Ravaged by disease, freezing to death in the bitter winter, lacking food or transport, harassed all the while by unsympathetic Albanian guerrillas, left with little or no hope to sustain them, the survivors managed somehow to stagger to the Albanian coast from where they could hope to be evacuated to safety by the Royal Navy.

In the Serbs’ wake the Austrian Third Army took possession of Montenegro, while the Bulgarians, whom neither the Germans nor Austrians wished to see established on the Adriatic, turned back from the border to join in the counter-offensive against the Entente invasion of Macedonia.

After the Bulgarians were defeated during the Vardar Offensive of September 1918, the Bulgarian Army collapsed, and with them came the collapse of the Central Powers in the Balkans. During October 1918 Serbian forces advanced toward Serbia liberating the country as the defeated Bulgarians and Austro-Hungarians retreated.

Although defeated by a combined Central Powers invasion, in the end the Serbs found themselves to be on the winning side of the war. After the war the Serbs would assume a leading role in the newly formed Kingdom of Yugoslavia.