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population because archaeology indicates a significant continuity of late antiquity population which have partially withdrawn to the mountains, coastal cities and islands.
South Slavs
East:
The Serbo-Croatian varieties have strong structural unity, and are regarded by most linguists as constituting one language. Today, language secessionism has led to several standards: Serbian, Croatian, Bosnian and Montenegrin, although the latter has historically and traditionally been called Serbian and is still undergoing standardization. Bosnian was officially established in 1996. These Serbo-Croatian standards are all based on the Shtokavian dialect group. Other dialect groups, which have lower intelligibility with Shtokavian, are Chakavian in Dalmatia and Kajkavian in Croatia proper. The dominance of Shtokavian in the Western Balkans is due to historical westward migration during the Ottoman period. Slovene is grouped into South Slavic, but has many features shared with West Slavic languages. The Prekmurje Slovene and Kajkavian are especially close, and there is no clear delineation between them. In southeastern Serbia, dialects enter a transitional zone with Bulgarian and Macedonian, with features of both groups, and is commonly called Torlakian.