Quick History
Serbia was occupied during the invasion of Yugoslavia and Greece in April 1941. The first occupation stamps and postcards were Yugoslavian pre-war issues which had been overprinted SERBIEN
which was the countries name in German and then from the end of 1941 most issues were new designs with the countries name in Serbian.

In the begining postal activity was wide spread, but within a few months partisan warfare made postal deliveries uncertain at best. Postal services were limited to the "Volksdeutsche" area of the Banat
(on the border with Hungary), Belgrade and some of the larger towns along the German supply routes to Greece. Stamps overprinted "BANAT" are not official overprints.