During World War II, several provinces of the Kingdom of Yugoslavia corresponding to the modern-day state of Serbia were occupied by the Axis Powers from 1941 to 1944. Most of the area was occupied by the Wehrmacht and was organized as separate territory under control of the German Military Administration in Serbia. Other parts of modern Serbia that were not included in the German-administered territory were occupied and annexed by neighboring Axis countries: Syrmia was occupied and annexed by the Independent State of Croatia, Bačka was occupied and annexed by Hungary, southeastern Serbia was occupied and annexed by Bulgaria, and southwestern Serbia was occupied and annexed by Italy and included in the Italian protectorates of Albania and Montenegro.
German occupation
The area under control of the German Military Administration in Serbia was initially occupied by the Germans. It was later occupied mostly by Bulgarian troops, but remained under German military authority. On stamps and coins this territory was referred to as Serbia, and, according Paul N. Hehn, its official name was the Territory of the Military Commander in Serbia. This territory had two successive Serbian puppet governments under the control of the German military authorities. The first, short-lived, puppet government was known as the Commissioner Government and was led by Milan Aćimović. The second puppet government was known as the Government of National Salvation and was led by Milan Nedić.
During the occupation, the Germans set up Soldatensender Belgrad, the popular radio station for German soldiers across Europe and Africa.
Approximately 11,000 of the Jewish population of about 12,500 in German-occupied Serbia, controlled by Hungary or the Independent State of Croatia, were murdered.
Italian-Albanian occupation
The line between the German-occupied area and the Italian Albania in the Kosovo region was the cause of a significant clash of interests, mainly due to the important lead and zinc mines at Trepča and the key railway line from Kosovska Mitrovica through Pristina–Uroševac–Kačanik to Skopje. Ultimately the Germans prevailed, with the "Vienna Line" extending from Novi Pazar in the Sandžak through Kosovska Mitrovica and Pristina, along the railway between Pristina and Uroševac and then towards Tetovo in modern-day North Macedonia before turning northeast to meet Bulgarian-annexed territory near Orlova Čuka. The Kosovska Mitrovica, Vučitrn and Lab districts, along with part of the Gračanica district, to were all part of the German-occupied territory. This territory contained a number of other important mines, including the lead mine at Belo Brdo, an asbestos mine near Jagnjenica and a magnesite mine at Dubovac near Vučitrn.
The Sandžak region was initially divided between the Germans in the north and the Italians in the south using an extension of the so-called "Vienna Line" which divided Yugoslavia into German and Italian zones of influence. The border of the occupied territory through the Sandžak was modified several times in quick succession during April and May 1941, eventually settling on the general line of Priboj–Nova Varoš–Sjenica–Novi Pazar, although the towns of Rudo, Priboj, Nova Varoš, Sjenica and Duga Poljana were on the Italian-occupied Montenegrin side of the border. The NDH government was unhappy with these arrangements, as they wanted to annex the Sandžak to the NDH and considered it would be easier for them to achieve this if the Germans occupied a larger portion of the region.
Hungarian occupation
After discussions with both the Romanian and Hungarian governments, Adolf Hitler decided that the Bačka and Banat region would be divided by the river Tisa, with the eastern portion under German occupation along with "Old Serbia". The portion west of the Tisa was occupied and annexed by Hungary. The Romanian-Hungarian rivalry was not the only reason for retaining the Banat under German occupation, as it also contained some 120,000 ethnic Germans (or Volksdeutsche) and was a valuable economic region. In addition to the Tisa, the other borders of the Banat were the Danube to the south, and the post-World War I Yugoslav-Romanian and Yugoslav-Hungarian borders in the north and east.