Serbian campaign
The Serbian campaign was a series of military expeditions launched in 1914 and 1915 by the Central Powers against the Kingdom of Serbia during the First World War. After an unsuccessful invasion by Austria-Hungary in 1914, the Central Powers launched a successful invasion in 1915 and occupied Serbia. In 1918, after breaking the front in Macedonia, Serbia and its allies liberated Serbia.
The first campaign began after Austria-Hungary declared war on Serbia on 28 July 1914. The campaign,
dubbed a "punitive expedition" by the Austro-Hungarian leadership, was under the command of Austrian General Oskar Potiorek. It ended after three unsuccessful Austro-Hungarian invasion attempts were repelled by the Serbians and their Montenegrin allies. The victory of the Royal Serbian Army at the battle of Cer is considered the first Allied victory in World War I, and the Austro-Hungarian Army's defeat by Serbia has been called one of the great upsets of modern military history.
The second campaign was launched, under German command, almost a year later, on 6 October 1915, when Bulgarian, Austro-Hungarian, and German forces, led by Field Marshal August von Mackensen, successfully invaded Serbia from three sides, pre-empting an Allied advance from Salonica to help Serbia. This resulted in the Great Retreat through Montenegro and Albania, the evacuation to Greece, and the establishment of the Macedonian front. The defeat of Serbia gave the Central Powers temporary mastery over the Balkans, opening up a land route from Berlin to Constantinople, allowing the Germans to re-supply the Ottoman Empire for the rest of the war. Mackensen declared an end to the campaign on 24 November 1915. Serbia was then occupied and divided between the Austro-Hungarian Empire and Bulgaria.
After the Allies launched the Vardar Offensive in September 1918, which broke through the Macedonian front and defeated the Bulgarians and their German allies, a Franco-Serbian force advanced into the occupied territories and liberated Serbia, Albania, and Montenegro. Serbian forces entered Belgrade on 1 November 1918.
The Serbian army declined severely from about 420,000 at its peak to about 100,000 at the moment of liberation. The estimates of casualties are various: Original Serb sources claim that the Kingdom of Serbia lost more than 1,200,000 inhabitants during the war, which represented more than 29% of its overall population and 60% of its male population. More recent historical analysis has estimated that roughly 177,000 Serbian soldiers lost their lives or were not returned from captivity, while the civilian death toll is impossible to determine, numbering in the hundreds of thousands. According to estimates prepared by the Yugoslav government in 1924, Serbia lost 265,164 soldiers or 25% of all mobilized troops. By comparison, France lost 16.8%, Germany 15.4%, Russia 11.5%, and Italy 10.3%.
Background
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 destabilized peace accords that were already unravelling in what was known as "the powder keg of Europe."File:G Princip.jpg|thumb|left|upright|Gavrilo Princip, a member of the Young Bosnia, assassinated Archduke Franz Ferdinand, the heir to the Austro-Hungarian throne
In 1912 and 1913, the First Balkan War was fought between the Balkan League of Greece, Bulgaria, Serbia, and Montenegro and the fracturing Ottoman Empire. The resulting Treaty of London further shrank the Ottoman Empire by creating an independent Principality of Albania and enlarging the territorial holdings of Bulgaria, Serbia, Montenegro, and Greece. When Bulgaria attacked both Serbia and Greece on 16 June 1913, it lost most of its Macedonian region to those countries, and additionally, the Southern Dobruja region to Romania and Adrianople to Turkey in the 33-day Second Balkan War, which further destabilized the region.
On 28 June 1914, Gavrilo Princip, a Bosnian Serb student and member of an organization of national revolutionaries called Young Bosnia, assassinated Archduke Franz Ferdinand of Austria, the heir to the Austro-Hungarian throne, in Sarajevo, Bosnia.
Though the political objective of the assassination was the independence of the southern Austro-Hungarian provinces mainly populated by Slavs from the Austro-Hungarian Empire, it also 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 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, drawing in Russia, Germany, France, and the British Empire. 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. Though Serbia had an experienced army, it was exhausted from the conflicts of the Balkan Wars and poorly equipped, which led the Austro-Hungarians to believe it would fall in less than a month. Serbia's strategy was to hold on as long as it could and hope the Russians could defeat the main Austro-Hungarian Army, with or without the help of other allies. 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.
Military forces
Austro-Hungarian
The standing peacetime Austro-Hungarian army had 36,000 officers, including non-commissioned officers and 414,000 enlisted personnel. During mobilization, this number could be increased to 3,350,000 men of all ranks. The operational army had over 1,420,000 men, while another 600,000 were allocated to support and logistic units. The rest were reserve troops available to replace losses and form new units. This vast military power allowed the Austro-Hungarian Army to replace its losses regularly and keep units at their formation strength. According to some sources, there were an average of 150,000 men per month during 1914 sent to replace the losses in the field army. During 1915 these numbers rose to 200,000 per month. According to the official Austrian documents in the period from September until the end of December 1914, some 160,000 replacement troops were sent to the Balkan theatre of war, as well as 82,000 reinforcements as part of newly formed units.The prewar Austro-Hungarian plan to invade Serbia envisioned the concentration of three armies on Serbia's western and northern borders to envelop and destroy the bulk of the Serbian army. However, with the beginning of the Russian general mobilization, the Armeeoberkommando decided to move the 2nd army to Galicia to counter Russian forces. Due to the congestion of railroad lines towards Galicia, the 2nd Army could only start its departure on 18 August, which allowed the AOK to assign some units of the 2nd Army to take part in operations in Serbia before that date. Eventually, the AOK allowed General Oskar Potiorek to deploy a significant segment of the 2nd army in fighting against Serbia, which caused a delay in the transport of these troops to the Russian front for more than a week. Furthermore, the Austro-Hungarian defeats suffered during the first invasion of Serbia forced the AOK to permanently transfer two divisions from the 2nd Army to Potiorek's force. By 12 August, Austria-Hungary had amassed over 500,000 soldiers on Serbian frontiers, including some 380,000 operational troops. However on 16 August a significant part of the 2nd army was ordered to the Russian front, thus this number fell to some 285,000 active troops, including garrisons. Apart from land forces, Austria-Hungary also deployed its Danube River flotilla of six monitors and six patrol boats.
Many Austro-Hungarian soldiers were not of good quality. About one-quarter of them were illiterate, and most of the conscripts from the empire's subject nationalities did not speak or understand German or Hungarian. In addition, most of the soldiers — ethnic Czechs, Slovaks, Poles, Romanians and South Slavs — had linguistic and cultural links with the empire's various enemies.
Serbian
The Serbian military command issued orders to mobilize its armed forces on 25 July, and mobilization began the following day. By 30 July, mobilization was completed, and the troops began to be deployed according to the war plan. Deployments were completed by 9 August when the troops had arrived at their designated strategic positions. During mobilization, Serbia raised approximately 450,000 men of three age-defined classes called poziv, which comprised all capable men between the ages of 21 and 45.The operational army consisted of infantry and one cavalry division. Aged men of the 3rd ban were organized in 15 infantry regiments with about 45–50,000 men designated for use in rear and line of communications duties. However, some of them were by necessity used as part of the operational army as well, bringing its strength up to around 250,000 men. Serbia was in a much more disadvantageous position when compared with Austria-Hungary concerning human reserves and replacement troops, as its only source of replacements were recruits reaching the age of military enlistment. Their maximum annual number was theoretically around 60,000 and was insufficient to replace the losses of more than 132,000 sustained during operations from August to December 1914. This shortage of military power forced the Serbian army to recruit under and over-aged men to make up for losses in the opening phase of the war.
Because of the poor financial state of the Serbian economy and losses in the recent Balkan Wars, the Serbian army lacked much of the modern weaponry and equipment necessary to engage in combat with their larger and wealthier adversaries. Only 180,000 modern rifles were available for the operational army, which meant that the Serbian military lacked between one-quarter to one-third of the rifles necessary to fully equip even their front-line units, let alone reserve forces. Although Serbia tried to remedy this deficit by ordering 120,000 rifles from Russia in 1914, the weapons did not begin to arrive until the second half of August. Only 1st ban troops had complete grey-green M1908 uniforms, with 2nd ban troops often wearing the obsolete dark blue M1896 issue, and the 3rd ban had no proper uniforms at all and were reduced to wearing their civilian clothes with military greatcoats and caps. The Serbian troops did not have service issued boots at all, and the vast majority of them wore everyday footwear made of pig skin called opanak.
Ammunition reserves were also insufficient for sustained field operations as most had been used in the 1912–13 Balkan wars. Artillery ammunition was sparse and only amounted to several hundred shells per unit. Because Serbia lacked a significant domestic military-industrial complex, its army depended entirely on imports of ammunition and arms from France and Russia, which were chronically short of supplies. The inevitable shortages of ammunition later would include a complete lack of artillery ammunition, which peaked during the decisive moments of the Austro-Hungarian invasion.