White Croats
It is considered that the Czech-Polish Croatian tribes were related to the Croatian tribes from Zakarpattia and Prykarpattia in Ukraine. They became separated during the migration period and seemingly formed one large Proto-Slavic tribe. It is theorized that the migration of those (White) Croatian tribes in the 7th century was the second and final Slavic migratory wave to the Balkans, which is related to the thesis by Bogo Grafenauer about the double migration of Slavs. According to this thesis, although it is possible that some Croatian tribes were present among Slavs in the first Slavic-Avar wave in the 6th century, it is argued that the Croatian migration in the second wave probably was not equally numerous to make a significant common-linguistical influence, while others considered they arrived in a significantly larger number. Zdenko Vinski and argued that the double migration thesis is supported by the rare findings of objects and ceramics of Prague-Korchak culture on the territory of Croatia, Bosnia and Herzegovina, and Serbia which were dated to the end of 6th and beginning of the 7th century (indicating first wave Slavs), and did not make a continuity with Slavic archaeological findings from the 8th-9th century, indicating assimilation. The Croatian tribes are also seen as a warrior group who assimilated into already present Slavs. In the territory of present-day Croatia they also gradually assimilated with the Pre-Slavic population because archaeology indicates a significant continuity of late antiquity population which have partially withdrawn to the mountains, coastal cities and islands.
Vlachs in the history of Croatia
In Serbian historiography all Dinaric/Shtokavian cultural attributes were without exception proclaimed as being Serb, and also often stressed the ethno-demographic discontinuity wanting to prove that the Croatian Military Frontier lost its original Croat population and received a new, ethnically Serb majority population, and also downplayed Croat and overemphasized the importance of the Serbs in the history of the Military Frontier. Serbian historiography strongly considered that the term Vlach indicated status and not ethnos, and that they didn't exist in later centuries as an ethnic group, yet were true Serbs. Sima Ćirković noted that the name was maintained due to different crafts, way of life and distinct form of social organization, until the differences lost their meaning, with Slavicization process lasting for centuries; he considered that Serbs absorbed many Vlachs and other ethnic groups. Many Serbian scholars, including foreign, claim that the settlers in the Military Frontier were Serbs or mainly Serbs.