The Kragujevac massacre was the mass murder of between 2,778 and 2,794 mostly Serb men and boys in Kragujevac by German soldiers on 21 October 1941. It occurred in the German-occupied territory of Serbia during World War II, and came as a reprisal for insurgent attacks in the Gornji Milanovac district that resulted in the deaths of ten German soldiers and the wounding of 26 others. The number of hostages to be shot was calculated as a ratio of 100 hostages executed for every German soldier killed and 50 hostages executed for every German soldier wounded, a formula devised by Adolf Hitler with the intent of suppressing anti-Nazi resistance in Eastern Europe.

After a punitive operation was conducted in the surrounding villages, during which over 400 males were shot and four villages burned down, another 70 male Jews and communists who had been arrested in Kragujevac were killed. Simultaneously, males between the ages of 16 and 60, including high school students, were assembled by German troops and local collaborators, and the victims were selected from amongst them. The selected males were then marched to fields outside the city, shot with heavy machine guns, and their bodies buried in mass graves. Contemporary German military records indicate that 2,300 hostages were shot. After the war, inflated estimates ranged as high as 7,000 deaths, but German and Serbian scholars have now agreed on the figure of nearly 2,800 killed, including 144 high school students. As well as Serbs, massacre victims included Jews, Romani people, Muslims, Macedonians, Slovenes, and members of other nationalities.

Several senior German military officials were tried and convicted for their involvement in the reprisal shootings at the Nuremberg trials and the subsequent Nuremberg trials. The massacre had a profound effect on the course of the war in Yugoslavia. It exacerbated tensions between the two guerrilla movements, the communist-led Partisans and the royalist, Serbian nationalist Chetniks, and convinced Chetnik leader Draža Mihailović that further attacks against the Germans would only result in more Serb civilian deaths. The Germans soon found mass executions of Serbs to be ineffectual and counterproductive, as they tended to drive the population into the arms of insurgents. The ratio of 100 executions for one soldier killed and 50 executions for one soldier wounded was reduced by half in February 1943, and removed altogether later in the year. The massacre is commemorated by the October in Kragujevac Memorial Park and the co-located 21 October Museum, and has been the subject of several poems and feature films. The anniversary of the massacre is commemorated annually in Serbia as the Day of Remembrance of the Serbian Victims of World War II.

Background Encirclement and invasion of Yugoslavia Following the 1938 between Nazi Germany and Austria, Yugoslavia came to share its northwestern border with Germany and fell under increasing pressure as its neighbours aligned themselves with the Axis powers. In April 1939, Italy opened a second frontier with Yugoslavia when it invaded and occupied neighbouring Albania. At the outbreak of World War II, the Yugoslav government declared its neutrality. Between September and November 1940, Hungary and Romania joined the Tripartite Pact, aligning themselves with the Axis, and Italy invaded Greece. Yugoslavia was by then almost completely surrounded by the Axis powers and their satellites, and its neutral stance toward the war became strained. In late February 1941, Bulgaria joined the pact. The following day, German troops entered Bulgaria from Romania, closing the ring around Yugoslavia. Intending to secure his southern flank for the impending attack on the Soviet Union, German dictator Adolf Hitler began placing heavy pressure on Yugoslavia to join the Axis. On 25 March 1941, after some delay, the Yugoslav government conditionally signed the pact. Two days later, a group of pro-Western, Serbian nationalist officers of the Royal Yugoslav Air Force deposed the country's regent, Prince Paul, in a bloodless coup d'état. They placed his teenage nephew, Peter, on the throne and brought to power a "government of national unity" led by the head of the Royal Yugoslav Air Force, General Dušan Simović. The coup enraged Hitler, who immediately ordered the country's invasion, which commenced on 6 April 1941.

Yugoslavia was quickly overwhelmed by the combined strength of the Axis powers and surrendered in less than two weeks. The government and royal family went into exile, and the country was occupied and dismembered by its neighbours. The German-occupied territory of Serbia was limited to the pre-Balkan War borders of the Kingdom of Serbia and was directly occupied by the Germans for the key rail and riverine transport routes that passed through it, as well as its valuable resources, particularly non-ferrous metals. The occupied territory covered about and had a population of 3.8 million. Hitler had briefly considered erasing all existence of a Serbian state, but this was quickly abandoned and the Germans began searching for a Serb suitable to lead a puppet government in Belgrade. They initially settled on Milan Aćimović, a staunch anti-communist who served as Yugoslavia's minister of internal affairs in late 1939 and early 1940.

Occupation and resistance

Two resistance movements emerged following the invasion: the communist-led, multi-ethnic Partisans, and the royalist, Serbian nationalist Chetniks, although during 1941, within the occupied territory, even the Partisans consisted almost entirely of Serbs. The Partisans were led by the General Secretary of the Communist Party of Yugoslavia, Josip Broz Tito; the Chetniks were led by Colonel Draža Mihailović, an officer in the interwar Royal Yugoslav Army. The two movements had widely divergent goals. Whereas the Partisans sought to turn Yugoslavia into a communist state under Tito's leadership, the Chetniks sought a return to the pre-war , whereby the Yugoslav monarchy—and, by extension, Serb political hegemony—would be restored. Communist resistance commenced in early July, shortly after the invasion of the Soviet Union, targeting both the Germans and the puppet authorities. By late August 1941, the Partisans and Chetniks were carrying out joint attacks against the Germans. The Partisans were well organised and many of their commanders had ample military experience, having fought in the Spanish Civil War. Within several months of the invasion, they had 8,000 fighters spread across 21 detachments in Serbia alone. Many Chetniks were either veterans of the Balkan Wars and World War I or former members of the Royal Yugoslav Army. They boasted around 20,000 fighters in the German-occupied territory of Serbia at the time of the massacre.

On 29 August, the Germans replaced Aćimović with another fervent anti-communist, the former Minister of the Army and Navy and Chief of the General Staff, General Milan Nedić, who formed a new puppet government. In September, the Nedić government was permitted to form the Serbian Volunteer Detachments (later Serbian Volunteer Corps, SDK), an auxiliary paramilitary formation to help quell anti-German resistance. In effect, the SDK was the military arm of the fascist Yugoslav National Movement (, Zbor), led by Dimitrije Ljotić. It was originally intended to have a strength of 3,000–4,000 troops, but this number eventually rose to 12,000. It was headed by Kosta Mušicki, a former colonel in the Royal Yugoslav Army, whom Nedić appointed on 6 October 1941. In the early stages of the occupation, the SDK formed the bulk of Nedić's forces, which numbered around 20,000 men by late 1941.

Prelude Anti-German uprising

Nedić's inability to crush the Partisans and Chetniks prompted the military commander in Serbia to request German reinforcements from other parts of the continent. In mid-September, they transferred the 125th Infantry Regiment from Greece and the 342nd Infantry Division from France to help put down the uprising in Serbia. On 16 September, Hitler issued Directive No. 312 to Generalfeldmarschall (field marshal) Wilhelm List, the Wehrmacht commander in Southeast Europe, ordering him to suppress all resistance in that part of the continent. That same day, the Supreme Command of the Armed Forces (Oberkommando der Wehrmacht; OKW) issued Hitler's order on the suppression of "Communist Armed Resistance Movements in the Occupied Areas", signed by Generalfeldmarschall Wilhelm Keitel. This decree specified that all attacks against the Germans on the Eastern Front were to be "regarded as being of communist origin", and that 100 hostages were to be shot for every German soldier killed and 50 were to be shot for every German soldier wounded. It was intended to apply to all of Eastern Europe, though an identical policy had already been implemented in Serbia as early as 28 April 1941, aimed at deterring guerrilla attacks. Attacks against the Germans increased in the first half of the year and Serbia once again became a war zone. German troops fanned through the countryside burning villages, taking hostages and establishing concentration camps. The first mass executions of hostages commenced in July.

The strengthening of Germany's military presence in Serbia resulted in a new wave of mass executions and war crimes. The commanders who bore the most responsibility for these atrocities were primarily of Austrian origin and had served in the Austro-Hungarian Army during World War I. Most were ardently anti-Serb, a prejudice that the historian Stevan K. Pavlowitch links to the Nazis' wider anti-Slavic racism. On 19 September, (lieutenant general) Franz Böhme was appointed as Plenipotentiary Commanding General in Serbia, with direct responsibility for quelling the revolt, bringing with him the staff of XVIII Mountain Corps. He was allocated additional forces to assist him in doing so, reinforcing the three German occupation divisions already in the territory. These divisions were the 704th Infantry Division, 714th Infantry Division and 717th infantry divisions. Böhme boasted a profound hatred of Serbs and encouraged his predominantly Austrian-born troops to exact "vengeance" against them. His primary grievances were the assassination of Archduke Franz Ferdinand and subsequent Austro-Hungarian military defeats at the hands of the Royal Serbian Army, which he thought could only be rectified by the reprisal shooting of Serbian civilians. "Your objective", Böhme declared, "is to be achieved in a land where, in 1914, streams of German blood flowed because of the treachery of the Serbs, men and women. You are the avengers of those dead."

Clashes at Gornji Milanovac Surrender of the 6th Company By late September 1941, the town of Gornji Milanovac had effectively been cut off from the rest of German-occupied Serbia by the frequent disruption of road and rail transport leading to and from it. On 29 September, elements of the Takovo Chetnik and Čačak Partisan detachments attacked Gornji Milanovac, which was defended by the 6th Company of the 920th (local defence) Battalion. The 6th Company's garrison was based out of a local school. The guerrillas did not expect to capture the garrison, but undertook the attack in order to generate new recruits from the surrounding area. The local Chetnik commander, Zvonimir Vučković, became aware of the Partisan plans and decided to join in the attack to avoid the significant loss of prestige that would result from allowing the Partisans to attack alone. The insurgents launched a morning attack against the school. Although they were successful in overrunning the sentry posts, the Germans' heavy machine guns soon stopped the assault. In 90 minutes of fighting, ten Germans were killed and 26 wounded. The two insurgent groups judged that continuing the assault would be too costly and Vučković suggested negotiating with the Germans.