The occupation began on 11 April 1941 when 80,000 Hungarian troops crossed the Yugoslav border in support of the German-led Axis invasion of Yugoslavia that had commenced five days earlier.

The occupation authorities immediately classified the population of Bačka and Baranja into those that had lived in those regions when they had last been under Hungarian rule in 1920 and the mostly Serb settlers who had arrived since the areas had been part of Yugoslavia.

They then began herding thousands of local Serbs into concentration camps and expelled them to the Independent State of Croatia, Italian-occupied Montenegro, and the German-occupied territory of Serbia.

This was followed by the implementation of a policy of "magyarisation" of the political, social and economic life of the occupied territories, which included the re-settlement of Hungarians and Székelys from other parts of Hungary.

Small-scale armed resistance to the Hungarian occupation commenced in the latter half of 1941 and was answered with harsh measures, including summary executions, expulsions and internment.

In March 1944, when Hungary realised that it was on the losing side in the war and began to negotiate with the Allies, Germany took control of the country, including the annexed territories, during Operation Margarethe I.

Prior to their withdrawal from the Balkans in the face of the advance of the Soviet Red Army, the Germans evacuated 60,000–70,000 Volksdeutsche from Bačka and Baranja to Austria.

At the Paris Peace Conference following the conclusion of World War I, the Entente Powers signed the Treaty of Trianon with Hungary after the breakup of Austria-Hungary.

[2][3] Between 1918 and 1924, 44,903 Hungarians (including 8,511 government employees) were deported to Hungary from the territories transferred to Yugoslavia, and approximately 10,000 Yugoslav military settlers (Serbo-Croatian: Solunski dobrovoljci, lit.

This census used language as the primary criterion, and counted all speakers of Serbo-Croatian as one group, rather than recognising distinct Serb, Croat, Bosnian Muslim, Macedonian and Montenegrin nationalities.

[36] During post-war questioning, Horthy insisted that he had not wished to invade Yugoslavia, but that he had been compelled to act by disorder and the massacre of Hungarians in Bačka, but these claims have been dismissed by Tomasevich.

[40] Lemkin asserted that "genocidal" policies were those that were aimed at destroying the political, social, cultural, religious, and economic existence and language of those living in occupied territories.

[11][51][52][53] During the war, the Hungarian government resettled some of its pre-war population in Bačka and Baranja, primarily Székelys from areas of Transylvania ceded to Hungary by Romania in 1940.

As part of the "systematic magyarisation" of these territories,[57] Hungarian political parties and patriotic organisations were encouraged to be active in Bačka and Baranja, which resulted in discrimination against "less-desirable elements" of the population such as Serbs, Croats and Jews.

[61] The Hungarian authorities referred to the occupied territories by the following names: Bácska for Bačka, Baranya for Baranja, Muraköz for Međimurje, and Muravidék for Prekmurje.

[62] Following the occupation, the Hungarian authorities divided the occupied territories between the counties that corresponded with the administrative divisions that had existed when the area had formed part of the Kingdom of Hungary prior to 1920.

[65] After small-scale armed resistance broke out in Hungarian-occupied Bačka and Baranja in the second half of 1941, the Hungarian military reacted with heavy repressive measures.

[35] Measures included the establishment of temporary concentration camps at Ada, Bačka Topola, Begeč, Odžaci, Bečej and Subotica, as well as at Novi Sad, Pechuj and Baja.

[66] In January 1942, the Hungarian army and gendarmerie undertook a major raid in southern Bačka, during which they massacred 2,550 Serbs, 743 Jews and 47 other people[67] in places such as Bečej, Srbobran and Novi Sad,[60][68] under the pretext that they were searching for Partisans.

Over the period 4–24 January, massacres were carried out by the Hungarian 15th Light Division commanded by Major General József Grassy and units of the Royal Gendarmerie.

The operations were ordered by Grassy, Lieutenant General Ferenc Feketehalmy-Czeydner, Colonel László Deák,[23] and Royal Gendarmerie Captain Dr. Márton Zöldi.

[71] In addition to Serbs and Jews, members of other ethnicities were also victims: Roma people, a small number of Russian refugees who had fled Russia after the Bolshevik Revolution, and some local Hungarians.

[76] Klajn believes that the massacre had been intended to convince the German Foreign Minister Joachim von Ribbentrop that Hungarian troops were needed on its territory instead of the Eastern Front.

Grassy became a SS-Gruppenführer und Generalleutnant der Waffen-SS (major general) and was appointed to command the 25th Waffen Grenadier Division of the SS Hunyadi (1st Hungarian), and Zöldi joined the Gestapo.

[83] Several days after the Soviet Red Army entered the Banat on 1 October 1944, the Germans began the evacuation of Bačka, including the local Volksdeutsche.

[86] After a few weeks, they withdrew and ceded full control of the region to the Partisans,[87] who established a military administration in the Banat, Bačka and Baranja on 17 October 1944.

[90] On 15 February 1945, the Banat, Bačka and Baranja were transferred from military to civilian administration with a People's Liberation Committee (Serbo-Croatian: Narodnooslobodilački odbor, NOO) taking control.

[92] In a third trial in early 1946, the National Court of Hungary in Budapest found Szombathelyi, Feketehalmy-Czeydner, Grassy, Deák, and Zöldi guilty of involvement in the massacres in the occupied territories, and in carrying out the deportation of Jews to extermination camps.

In accordance with the provisions of Article 14 of the Armistice Agreement, the Hungarian authorities then extradited them to Yugoslavia, where they underwent a fourth trial in Novi Sad in October 1946.

[95] Of the approximately 500,000 Volksdeutsche living in Yugoslavia before the war, about half were evacuated, 50,000 died in Yugoslav concentration camps, 15,000 were killed by the Partisans and about 150,000 were deported to the Soviet Union as forced labourers.