It formed part of the 2nd Army Group, and was responsible for the defence of the section of the Yugoslav-Hungarian border between the Danube and the Tisza rivers.

The Germans closed on Sarajevo, and accepted the unconditional surrender of the Royal Yugoslav Army on 17 April, which came into effect at the following day.

The Kingdom of Serbs, Croats and Slovenes was created with the merger of Serbia, Montenegro and the South Slav-inhabited areas of Austria-Hungary on 1 December 1918, in the immediate aftermath of World War I.

The army budget remained tight, and as tensions rose across Europe during the 1930s, it became difficult to secure weapons and munitions from other countries.

[4] Consequently, at the time World War II broke out in September 1939, the VKJ had several serious weaknesses, which included reliance on draught animals for transport, and the large size of its formations.

[8][9] The weaknesses of the VKJ in strategy, structure, equipment, mobility and supply were exacerbated by serious ethnic disunity within Yugoslavia, resulting from two decades of Serb hegemony and the attendant lack of political legitimacy achieved by the central government.

[17] The following day, the situation deteriorated significantly when the German XLI Motorised Corps crossed the Yugoslav-Romanian border into the Yugoslav Banat and struck the 6th Army, halting its withdrawal and disrupting its ability to organise a coherent defence behind the Danube.

The 8th Panzer Division turned southeast between the Drava and Sava rivers, and meeting almost no resistance and with strong air support, had reached Slatina by evening, despite poor roads and bad weather.

[19] Later that day, as the situation was becoming increasingly desperate throughout the country, Dušan Simović, who was both the Prime Minister and Yugoslav Chief of the General Staff, broadcast the following message:[19] All troops must engage the enemy wherever encountered and with every means at their disposal.

Don't wait for direct orders from above, but act on your own and be guided by your judgement, initiative, and conscience.The bulk of the 1st Army were able to cross the Danube and began to prepare defences.

[26] On the night of 11/12 April, the 8th Panzer Division captured Sremska Mitrovica on the Sava at 02:30,[19] destroyed a bridge over the Danube at Bogojevo,[27] and advanced on Lazarevac about 32 kilometres (20 mi) south of Belgrade.

[27] West of Belgrade, remnants of the 2nd Army Group tried to establish a line along the Sava, but XLVI Motorised Corps had already captured the bridges.

[32] Shortly after takeoff from the airport at Veszprém-Jutas on the afternoon of 12 April, the command plane, code E-101, crashed with the loss of 20[33] or 23 lives, including 19 paratroopers.

Elements of the 8th Panzer Division did continue their thrust to capture the Sava bridges to the west of Belgrade, and entered the city during the night.

[36] On 14 and 15 April, tens of thousands of Yugoslav soldiers were taken prisoner by the Germans during their drive on Sarajevo in the centre of the country, including 30,000 around Zvornik and 6,000 around Doboj.