Austria-Hungary precipitated the Bosnian crisis of 1908-09 by annexing the former Ottoman territory of Bosnia and Herzegovina, which it had occupied since 1878. This angered the Kingdom of Serbia and its patron, the Pan-Slavic and Orthodox Russian Empire. Russian political manoeuvring in the region destabilised peace accords that were already unravelling in what was known as “the powder keg of Europe”.

After the Balkan Wars the Black Hand represented a core of military opposition to the civil assembly. Acting from within the government and the military, members of The Black Hand forced Peter to disband the government of Nikola Pasic, even though the Radical Party held most of the seats in the National Assembly. Only just after Russian intervention and with the help of the French capital, the crisis was solved in Pasic’s favour. King Peter had to withdraw, allegedly because of his failing health, and, on 24 June 1914, he passed his royal powers to his heir, Alexander I Karadjordjevic, who became Regent of Serbia and the Supreme Commander of the Serbian Army.

On 28 June 1914, Gavrilo Princip, a Bosnian Serb student and member of a multi-ethnic organisation of national revolutionaries called Young Bosnia, assassinated Archduke Franz Ferdinand of Austria, the heir to the Austro-Hungarian throne, in Sarajevo, Bosnia. Young Bosnia’s political objective was the independence of the southern Austro-Hungarian provinces mainly populated by Slavs from the Austro-Hungarian Empire. The assassination inadvertently triggered a chain of events that embroiled Russia and the major European powers. This began a period of diplomatic manoeuvring among Austria-Hungary, Germany, Russia, France, and Britain called the July Crisis. Austria-Hungary delivered the July Ultimatum to Serbia, a series of ten demands intentionally made unacceptable in order to provoke a war with Serbia. When Serbia agreed to only eight of the ten demands, Austria-Hungary declared war on 28 July 1914.

The dispute between Austria-Hungary and Serbia escalated into what is now known as World War I, and drew in Russia, Germany, France, and the United Kingdom. Within a week, Austria-Hungary had to face a war with Russia, Serbia’s patron, which had the largest army in the world at the time. The result was that Serbia became a subsidiary front in the massive fight that started to unfold along Austria-Hungary’s border with Russia. Serbia constantly had to worry about its hostile neighbour to the east, Bulgaria, with which it had fought several wars, most recently in the Second Balkan War of 1913.

The Serbian military command issued orders for the mobilization of its armed forces on 25 July and the mobilization began the following day. By 30 July, the mobilization was completed and the troops began to be deployed according to the war plan. Deployments were completed by 9 August, when all of the troops had arrived at their designated strategic positions. During mobilization, Serbia raised approximately 450,000 men of three age-defined classes or bans called poziv, which comprised all able-bodied men between 21 and 45 years of age, comprising four armies – the First Army, commanded by general Petar Bojovic, the Second Army, commanded by general Stepa Stepanovic,the Third Army, commanded by general Pavle Jurisic Sturm and the Uzice Army, commanded by general Milos Bozanovic.

Serbia entered World War I with battle-hardened, outstandingly well-educated officer corps and extremely motivated, well-trained troops, who emerged victorious in two wars only a couple of years before. The Kingdom of Serbia was at the height of its economic and political prosperity, which all made it a formidable opponent.

The Serbian campaign started on 28 July 1914, when Austria-Hungary declared war on Serbia and her artillery shelled Belgrade the following day. On August 12 the Austro-Hungarian armies crossed the border, the Drina River.

The Fifth and Sixth Austro-Hungarian Armies had about 270,000 men. Overall Austro-Hungarian command was in the hands of General Potiorek. The Austro-Hungarian Empire had the third largest population in Europe in 1914, behind Russia and Germany (almost twelve times the population of the Kingdom of Serbia), giving it an enormous manpower advantage.

Battle of Cer

Potiorek rushed the attack against Serbia from northern Bosnia with his Fifth Army, supported by elements of the Second Army from Syrmia. The Second Army was due to be transported to Galicia to face the Russians at the end of August, but he made use of it until then. The Sixth was positioning itself in southern Bosnia and was not yet able to commence offensive operations. Potiorek’s desire was to win a victory before Emperor Franz Joseph’s birthday and to knock Serbia out as soon as possible. Thus he made two grave strategic errors by attacking with only just over half of his strength and attacking hilly western Serbia instead of the open plains of the north. This move surprised Marshal Putnik, who expected attack from the north and initially believed that it was a feint. Once it became clear that it was the main thrust, the strong Second Army under the command of General Stepa Stepanovic was sent to join the small Third Army under Pavle Jurisic Sturm already facing the Austro-Hungarians and expel the invaders. After a fierce four-day battle, the Austro-Hungarians were forced to retreat, marking the first Allied victory of the war over the Central Powers led by Germany and Austria-Hungary.

Battle of Drina

Under pressure from its allies, Serbia conducted a limited offensive across the Sava River into the Austro-Hungarian region of Syrmia with its First Army. The main operational goal was to delay the transport of the Austro-Hungarian Second Army to the Russian front. The objective was shown to be futile as Austro-Hungarian forces were already in transport. Meanwhile, the Timok division I of the Serbian Second Army suffered a heavy defeat in a diversionary crossing.

With most of his forces in Bosnia, Potiorek decided that the best way to stop the Serbian offensive was to launch another invasion into Serbia to force the Serbs to recall their troops to defend their much smaller homeland.

7 September brought a renewed Austro-Hungarian attack from the west, across the river Drina, this time with both the Fifth Army in Macva and the Sixth further south. The initial attack by the Fifth Army was repelled by the Serbian Second Army, but the stronger Sixth Army managed to surprise the Serbian Third Army and gain a foothold. After some units from the Serbian Second Army were sent to bolster the Third, the Austro-Hungarian Fifth Army also managed to establish a bridgehead with a renewed attack. At that time, Marshal Putnik withdrew the First Army from Syrmia (against much popular opposition) and used it to deliver a fierce counterattack against the Sixth Army that initially went well, but finally bogged down in a bloody four-day fight for a peak of the Jagodnja mountain called Mackov Kamen, in which both sides suffered horrendous losses in successive frontal attacks and counterattacks.

Marshal Putnik ordered a retreat into the surrounding hills and the front settled into a month and a half of trench warfare, which was highly unfavourable to the Serbs, who had little in the way of an industrial base and were deficient in heavy artillery, ammunition stocks and shell production. Most of their war material was supplied by the Allies, who were short of such materials themselves. In such a situation, Serbian artillery quickly became almost silent, while the Austro-Hungarians steadily increased their fire.

During the first weeks of trench warfare, the Serbian Uzice Army (first strengthened division) and the Montenegrin Sanjak Army (roughly a division) conducted an abortive offensive into Bosnia. In addition, both sides conducted a few local attacks, most of which were soundly defeated. In one such attack, the Serbian Army used mine warfare for the first time: the Combined Division dug tunnels beneath the Austro-Hungarian trenches (that were only 20–30 meters away from the Serbian ones on this sector), planted mines and set them off just before an infantry charge.

Battle of Kolubara

Having thus weakened the Serbian army, the Austro-Hungarian Army launched another massive attack on 5 November. The Serbs withdrew step by step, offering strong resistance at the Kolubara River, but to no avail, due to the lack of artillery ammunition. It was at that time that General Zivojin Misic was made commander of the battered First Army, replacing the wounded Petar Bojovic. He insisted on a deep withdrawal in order to give the troops some much-needed rest and to shorten the front. Marshal Putnik finally relented, but the consequence was the abandonment of the capital city of Belgrade. After suffering heavy losses, the Austro-Hungarian Army entered the city on 2 December. This action led Potiorek to move the whole Fifth Army into the Belgrade area and use it to crush the Serbian right flank. This, however, left the Sixth alone for a few days to face the whole Serbian army.

At this point, artillery ammunition finally arrived from France and Greece. In addition, some replacements were sent to the units and Marshal Putnik correctly sensed that the Austro-Hungarian forces were dangerously overstretched and weakened in the previous offensives, so he ordered a full-scale counterattack with the entire Serbian Army on 3 December against the Sixth Army. The Fifth hurried its flanking manoeuvre, but it was already too late – with the Sixth Army broken, the Second and Third Serbian Armies overwhelmed the Fifth. Finally, Potiorek lost his nerve and ordered yet another retreat back across the rivers into Austria-Hungary’s territory. The Serbian Army recaptured Belgrade on 15 December.

The first phase of the war against Serbia had ended with no change in the border, but casualties were enormous compared to earlier wars, albeit comparable to other campaigns of World War I. Austro-Hungarian General Potiorek was removed from command and replaced by Archduke Eugen of Austria. On the Serbian side, a deadly typhus epidemic killed hundreds of thousands of Serb civilians during the winter.

After the Battle of Kolubara, the Serbian Parliament adopted the Nis Declaration (7 December 1914) on the war goals of Serbia: “Convinced that the entire Serbian nation is determined to persevere in the holy struggle for the defence of their homesteads and their freedom, the government of the Kingdom (of Serbia) considers that, in these fateful times, its main and only task is to ensure the successful completion of this great warfare which, at the moment when it started, also became a struggle for the liberation and unification of all our unliberated Serbian, Croatian and Slovenian brothers. The great success which is to crown this warfare will make up for the extremely bloody sacrifices which this generation of Serbs is making”. This amounted to announcing Serbia’s intention to annex extensive amounts of Austria-Hungary’s Balkan provinces.

1915

Early in 1915, with Ottoman defeats at the Battle of Sarikamish and in the First Suez Offensive, the German Chief of the General Staff Erich von Falkenhayn tried to convince the Austro-Hungarian Chief of Staff, Conrad von Hötzendorf, of the importance of conquering Serbia. If Serbia were taken, then the Germans would have a direct rail link from Germany through Austria-Hungary, then down to Istanbul and beyond. This would allow the Germans to send military supplies and even troops to help the Ottoman Empire. While this was hardly in Austria-Hungary’s interests, the Austro-Hungarians did want to defeat Serbia. However, Russia was the more dangerous enemy, and furthermore, with the entry of Italy into the war on the Allied side, the Austro-Hungarians had their hands full.

Both the Allies and the Central Powers tried to get Bulgaria to pick a side in the Great War. Bulgaria and Serbia had fought two wars in the last 30 years: the Serbo-Bulgarian War in 1885, and the Second Balkan War in 1913. The result was that the Bulgarian government and people felt that Serbia was in possession of lands to which Bulgaria was entitled, and when the Central Powers offered to give them what they claimed, the Bulgarians entered the war on their side. With the Allied loss in the Gallipoli campaign and the Russian defeat at Gorlice, King Ferdinand of Bulgaria signed a treaty with Germany and on 23 September 1915, Bulgaria began mobilizing for war.

Against Serbia were marshalled the Bulgarian First Army, the German Eleventh Army and the Austro-Hungarian Third Army, all under the control of Field Marshal August von Mackensen. In addition the Bulgarian Second Army, which remained under the direct control of the Bulgarian high command, was deployed against Macedonia.

Great Retreat

The Austro-Hungarians and Germans began their attack on 7 October with their troops crossing the Drina and Sava rivers, covered by heavy artillery fire. Once they crossed the Danube, the Germans and Austro-Hungarians moved on Belgrade itself. Vicious street fighting ensued, and the Serbs’ resistance in the city was finally crushed on 9 October.

Then, on 14 October, the Bulgarian Army attacked from the north of Bulgaria towards Nis and from the south towards Skopje. The Bulgarian First Army defeated the Serbian Second Army at the Battle of Morava, while the Bulgarian Second Army defeated the Serbians at the Battle of Ovche Pole. With the Bulgarian breakthrough, the Serbian position became untenable; the main army in the north (around Belgrade) could either retreat or be surrounded and forced to surrender. In the Battle of Kosovo, the Serbs made a last and desperate attempt to join the two incomplete Allied divisions that made a limited advance from the south, but were unable to gather enough forces due to the pressure from the north and east. They were halted by the Bulgarians and had to pull back.

Marshal Putnik ordered the Great Retreat, a full retreat south and west through Montenegro and into Albania. The weather was terrible, the roads poor, and the army had to help the tens of thousands of civilians who retreated with them with almost no supplies or food left. But the bad weather and poor roads worked for the refugees as well, as the Central Powers forces could not press them hard enough, so they evaded capture. Many of the fleeing soldiers and civilians did not make it to the coast, though – they were lost to hunger, disease, and attacks by enemy forces and Albanian tribal bands.

The circumstances of the retreat were disastrous. All told, only some 155,000 Serbs, mostly soldiers, reached the coast of the Adriatic Sea and embarked on Allied transport ships that carried the army to various Greek islands (mainly to Corfu) before being sent to Salonika. The evacuation of the Serbian army from Albania was completed on 10 February 1916. The survivors were so weakened that thousands of them died from sheer exhaustion in the weeks after their rescue. Marshal Putnik had to be carried during the whole retreat and he died around fifteen months later in a hospital in France.

The French and British divisions had marched north from Thessaloniki in October 1915 under the command of French General Maurice Sarrail. The War Office in London was reluctant to advance too deep into Serbia, so the French divisions advanced on their own up the Vardar River. This advance gave some limited help to the retreating Serbian Army, as the Bulgarians had to concentrate larger forces on their southern flank to deal with the threat, which led to the Battle of Krivolak (October-November 1915). By the end of November, General Sarrail had to retreat in the face of massive Bulgarian assaults on his positions. During his retreat, the British at the Battle of Kosturino were also forced to retreat. By 12 December, all allied forces were back in Greece.

Macedonian Front and Liberation of Serbia

The Serbian army was evacuated to Greece and joined up with the Allied Army of the Orient. They then fought a trench war against the Bulgarians on the Macedonia Front (also known as the Salonika Front). The Macedonian Front in the beginning was mostly static. French and Serbian forces re-took limited areas of Macedonia by recapturing Bitola on 19 November 1916 as a result of the costly Monastir Offensive, which brought stabilization of the front.

French and Serbian troops finally made a breakthrough in the Vardar Offensive in 1918, after most of the German and Austro-Hungarian troops had withdrawn. This breakthrough was significant in defeating Bulgaria and Austria-Hungary, which led to the final victory of World War I. After the Allied breakthrough, Bulgaria capitulated on 29 September 1918. Hindenburg and Ludendorff concluded that the strategic and operational balance had now shifted decidedly against the Central Powers and insisted on an immediate peace settlement during a meeting with government officials a day after the Bulgarian collapse. On 29 September 1918, the German Supreme Army Command informed Kaiser Wilhelm II and the Imperial Chancellor Count Georg von Hertling, that the military situation facing Germany was hopeless.

The collapse of the Macedonian front meant that the road to Budapest and Vienna was now opened for the 670,000-strong army of General Franchet d’Esperey as the Bulgarian surrender deprived the Central Powers of the 278 infantry battalions and 1,500 guns (the equivalent of some 25 to 30 German divisions) that were previously holding the line. The German high command responded by sending only seven infantry and one cavalry division, but these forces were far from enough for a front to be re-established.

Serbs, with their well-earned reputation, spearheaded the attack of the Allied armies, mostly French but aided by British and Greek troops. They pushed forward in September 1918, forced Bulgaria to leave the war and eventually managed to liberate Serbia two weeks before the end of World War I.

End of the War

The ramifications of the war were manifold. When World War I ended, the Treaty of Neuilly awarded Western Thrace to Greece, whereas Serbia received some minor territorial concessions from Bulgaria. Austria-Hungary was broken apart, and Hungary lost much land to both Yugoslavia and Romania in the Treaty of Trianon. Serbia assumed the leading position in the new Kingdom of Yugoslavia, joined by its old ally, Montenegro.