During the occupation, between 150,000 and 200,000 men, women and children were deported to purpose-built internment and concentration camps in Austria-Hungary, most notably Mauthausen in Austria, Doboj in Bosnia, and Nagymegyer, Arad and Kecskemét in Hungary.

The Austro-Hungarian military leadership was determined to quash Serbia's independence, which it viewed as an unacceptable threat to the future of the empire given its sizeable South Slavic population.

That evening, Austro-Hungarian artillery shelled the Serbian capital of Belgrade from the border town of Semlin (modern-day Zemun), effectively starting World War I.

Command of the Austro-Hungarian invasion force was delegated to Feldzeugmeister Oskar Potiorek, the Governor-General of Bosnia and Herzegovina, who had been responsible for the security of Franz Ferdinand and his wife Duchess Sophie of Hohenberg in Sarajevo.

On 17 August 1914, in the Serbian town of Šabac, 120 residents—mostly women, children and old men, who had previously been locked in a church—were shot and buried in the churchyard by Austro-Hungarian troops on the orders of Feldmarschall-Leutnant Kasimir von Lütgendorf.

[6] These types of attacks were planned at the highest level, the ground for the escalation of violence was ideologically prepared by the commanders' verbal radicalism,[8] on August 13 Potiorek ordered reprisal hangings, the taking of hostages and arson by all units.

[6] Often bodies were left hanging on the gallows, trees or street lamps for days as a deterrent and as evidence of the Austro-Hungarian military's determination to deal with Serbian suspects.

[15] American war correspondent John Reed, touring Serbia with Canadian artist Boardman Robinson, reported stories about the atrocities committed by Austrian soldiers against the civilian population "We saw the gutted Hôtel d’Europe, and the blackened and mutilated church in Šabac where three thousand men, women and children were penned up together without food or water for four days, and then divided into two groups – one sent to Austria as prisoners of war, the other driven ahead of the army as it marched south against the Serbians".

[18][19] On 24 August, after delivering a major defeat to Austria-Hungary's invading "Balkan Armed Forces" (German: Balkanstreitkräfte) at the Battle of Cer,[11] the Royal Serbian Army liberated Šabac and reached the frontier banks of the Sava River, thereby bringing the first Austro-Hungarian invasion of Serbia to an end, and securing the first Allied victory of World War I.

The Austro-Hungarian Feldmarschall of Croatian ethnicity Stjepan Sarkotić, commander during the first invasion of the 42nd Home Guard Infantry Division,[11] was appointed governor-general of Serbia by Emperor Franz Joseph on 24 November 1914.

[26] In early December, the Royal Serbian Army launched a sustained counterattack, decisively defeating the Austro-Hungarians at the Battle of Kolubara and recapturing Belgrade a day after General Sarkotic's new military government had been established.

[39] On 21 October Skopje is occupied by Bulgarian troops effectively cutting off the Serbian Army's lines of communication to the south as well as a retreat route towards French General Maurice Sarrail's relief force, which had advanced northwards up the Vardar River valley from the Allies' new base in Salonica.

[44] While the strategic goals set before the offensive had been achieved, the Central Powers were deprived of a decisive victory by the Royal Serbian Army's winter retreat over the mountains of Albania and Montenegro towards the Adriatic coast.

[49] The first governor-general, Johann Graf Salis-Seewis, an ethnic Croat with experience fighting insurgents in Macedonia, had served as the commander of the 42nd Devil's Division after Sarkotić.

Four administrative departments were set up: military, economic, judicial, and political, with the latter, which had its own intelligence and police forces, under former Devil's Division officer and future Ustaše[b] leader Major Slavko Kvaternik.

MGG/S control over the population was accomplished in accordance with the "Directives for the Political Administration in the Areas of the General Military Governorate in Serbia" (German: Direktiven für die politische Verwaltung im Bereiche des Militärgeneralgouvernements in Serbien) and with the "General Principles for the Imperial and Royal Military Administration in the Occupied Territories of Serbia" (German: Allgemeine Grundzüge für die K.u.K Militärverwaltung in den besetzten Gebieten Serbiens).

[56] The MGG/S intended to ignore Hungarian objections and integrate Serbia as a part of the empire, but as an area that would remain under direct military rule for decades after the end of the war and where political participation would be prohibited to prevent the emergence of a new Serbian state.

[58] To help police the civilian population and to track down partisans, the Austro-Hungarian leadership decided to recruit among ethnic minority groups positively disposed towards the Dual Monarchy.

[68] These counter-insurgency bands were based on their Bosnian counterparts, the Streifkorps, paramilitary groups made up of Muslim volunteers with experience fighting Serb guerrillas and a reputation for heavy-handed tactics.

"[73] Tisza refused to consider the annexation of Serbia as it would lead to a substantial increase in Austria-Hungary's Slavic population, and significantly reduce the proportion of Hungarians within the Dual Monarchy.

[72] After touring the three northwestern districts of Serbia together with Salis-Seewis and the visiting General Conrad, Tisza came to regard the Austro-Hungarian military's efforts in the occupied territory as a prelude to annexation.

[55] Tisza submitted a complaint to Burián asking for a thorough reorganisation of the Military Governorate, the removal of Salis-Seewis, whose administration he described as "Serbophile and economically incompetent",[74] and requesting the condemnation of those demanding that Serbia be annexed.

[101] The camp at Heinrichsgrün (modern-day Jindřichovice, Czech Republic), held mostly Serbs, both soldiers and civilians, from the Šumadija and Kolubara districts of western Serbia.

The Spanish authorities complained then, in April 1917, the Holy See intervened through the office of the Apostolic Nunciature to Austria against the internment of Serbian women and children between the ages of 10 and 15.

"[114][f] This portrayal largely stemmed from Austro-Hungarian propaganda aimed at sustaining morale in the Habsburg hinterland by presenting occupied Serbia as a success story.

[113] Travel reports by journalists such as Hans Richter described Serbia as a "garden of paradise" and confidently predicted it could become "the breadbasket of Europe," feeding not only the army but also Austro-Hungarian civilians.

[119] Immediately after the withdrawal of the Royal Serbian Army and the start of the Austro-Hungarian occupation, armed individuals and small groups of insurgents, called Chetniks, made up of former soldiers who had remained in the country, began to wage a guerrilla campaign against the occupiers.

[123] The Military Governorate responded to the multiplication of guerrilla groups by employing small Ottoman and Albanian counter-guerrilla units based on the Streifkorps from Bosnia instead of regular patrol troops.

[68] In late September 1916, the Serbian High Command flew in the experienced Chetnik guerrilla leader Kosta Pećanac from Allied Headquarters in Salonica.

[127] After the war, Chief of Staff Paul Kirch described the withdrawal of the German 11th Army:Serb guerrilla groups emerged throughout the country and attacked our units when they were resting or eating.