The border between Hungary and Kingdom of Serbs, Croats and Slovenes was finally regulated by the Treaty of Trianon on June 4, 1920.
The territory inhabited by Slovenes (the so-called Vendvidék) was divided by the watershed of the two rivers Rába and Mura.
After the German invasion of Yugoslavia in 1941, Hungary annexed the regions lost in 1920 including Slovenian Prekmurje.
Sándor Mikola, a well-known Hungarian physicist hailing from Slovenian Prekmurje, used his influence to publicize this view in his book A Vendség múltja és jelene (The past and present of the Wends).
Prekmurje remained a part of SFR Yugoslavia and SR Slovenia when the Trianon boundaries were restored after World War II.