By the 11th century, the Germanization of what is now Lower Austria , effectively isolated the Slovene-inhabited territory from the other western Slavs , speeding up the development of the Slavs of Carantania and of Carniola into an independent Carantanian/Carniolans/Slovene ethnic group. By the late Middle Ages, the historic provinces of Carniola, Styria , Carinthia , Gorizia , Trieste , and Istria developed from the border regions and were incorporated into the medieval German state. The consolidation and formation of these historical lands took place in a long period between the 11th and 14th centuries, and were led by a number of important feudal families, such as the Dukes of Spannheim , the Counts of Gorizia , the Counts of Celje , and, finally, the House of Habsburg . In a parallel process, an intensive German colonisation significantly diminished the extent of Slovene-speaking areas. By the 15th century, the Slovene ethnic territory was reduced to its present size.