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population because archaeology indicates a significant continuity of late antiquity population which have partially withdrawn to the mountains, coastal cities and islands.
Dalibor Brozović
Instead of "Serbo-Croatian", Brozović preferred the term "Central South Slavic diasystem", asserting separate language status for Croatian and Serbian. However, Brozović advocated the term "Croato-Serbian" even in 1988. As far as language status is concerned, Brozović has asserted for nearly three decades that "the Serbian and Croatian variants are (...) phenomenons, which are analogous to the English and American variants"; "As in other cases where several nations use one standard language (German, Dutch, English, French, Spanish, Portuguese standard language), the standard Croato-Serbian language is not unified. In linguistics (especially in sociolinguistics), the realizations of such standard languages are called "variants of a standard language"". Brozović maintained that it is "a fact that Serbs and Croats have a common language", and he described it as pluricentric even in 1992. In the 1990s, Brozović became one of the leading proponents of linguistic purism in Croatia.