There is an opinion by many experts in the Slavic studies that ancient Sarmatians, Scythians, and Antes were the Slavs and, therefore, proto-Croats and proto-Serbs maybe parts of them. In addition, most probably that ancient Balkan Illyrians of the Indo-European origin, dominating the Central and West Balkans, have been, in fact, autochtonous Slavs of South-East Europe.
The ideology of Pan-Croatianism created by Pavao Ritter Vitezović, who developed the ancient theory upon derivation of all Slavs from the Balkans, was a historical construction and a political program as a protest against long-time fragmentation of alleged Croatian historical and ethnic territories.
It is not surprising that Pavao Ritter Vitezović interpolated the whole territory of the Kingdom of Poland and the Grand Duchy of Lithuania into the Slavic lands, and furthermore, according to his ideological doctrine into a Greater Croatia.
Basically, Vitezović’s idea was to ideologically pave the road to the creation of a unified Croatia with the help of the Habsburg foreign policy as all South Slavs and their lands were already before the Great Vienna War considered by Vienna to be within the Habsburg sphere of interest.
The real ideological source for such a division of the whole world was the Slavic idea which decisively influenced Vitezović who recognized that all Slavs belonged to a single ethnolinguistic community.
The issue of national self-determination, the idea and goals of nationhood, and the methods and means for the attainment of such goals, were foremost in the thinking of 19th-century Serbian intellectuals and politicians.
The national dream of a free and united Serbian state began to be realized at the beginning of the 19th century, with two Serbian insurrections against the Ottoman authorities in 1804–1813 and 1815.
Russia And The Balkans (1804): A Program About Slavonic-Serbian State Under The Russian Protectorate (II)
The Karlovci Metropolitan Stevan Stratimirović created the idea of autonomous tributary religion-language-based Orthodox Shtokavian Slavonic–Serbian state in 1804. His concept of a politically united religion-language-based Serbian nation within the borders of a single national state anticipated unification of the historical and ethnic Serbian territories from both the Ottoman Empire and the Habsburg Monarchy.
Russia And The Balkans (1804): A Program About Slavonic-Serbian State Under The Russian Protectorate (I)
Imperial Russia as an Orthodox country and the country with the largest Slavic population gradually inspired the spiritual-political leader of the Serbian nation during the Habsburg and Ottoman lordships, to believe that only the Romanovs could be real liberators and protectors of the Serbs and the rest of the South-Slavs, especially the Orthodox ones.
There were many variations of the project of the unification of the South Slavic or Yugoslav lands towards the end of the 19th century. However, in all of such projects of a Greater Yugoslavia, Serbia was seen as a Yugoslav Piedmont with Belgrade as the “Serbian Bismarckism”.
The development of the “Idea of Union”, i.e. of bringing all South Slavs into one state, originated from the idea of South Slavic common ethnic, historical and linguistic origins, which can be historically traced from the end of the 18th century.