Postage stamps and postal history of Yugoslavia
The story of the postage stamps and postal history of Yugoslavia officially begins with the formation of the Kingdom of Serbs, Croats and Slovenes on 1 December 1918. == Formation == Prior to the formation of the Kingdom, each of the constituent territories had their own postal systems and history.
Source: Wikipedia — Postage stamps and postal history of Yugoslavia (CC BY-SA 4.0)