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population because archaeology indicates a significant continuity of late antiquity population which have partially withdrawn to the mountains, coastal cities and islands.
Origin hypotheses of the Croats
Anthropologically, the craniometrical measurements made on the contemporary Croatian population of the city of Zagreb showed it is predominantly dolichocephalic, more specifically mesocephalia and leptoprosopia prevail in South Dalmatia, and brachycephaly and euryprosopy in Central Croatia. According to the 1998-2004 craniometric study of medieval Central European archaeological sites, four Dalmatian and two Bosnian sites clustered with Polish sites, two Continental Croatia (Avaro-Slav) sites were classified into the cluster of Hungarian sites west of the Danube, while the two sites from the Bijelo Brdo culture were into the cluster of Slav sites from Austria, the Czech Republic, and Slovenia. Comparison to the Scythian-Sarmatian sites did not reveal significant similarity in cranial morphology, nor was supported the idea of the Avar frontiersmen. The results indicate that the nucleus of the early Croat state in Dalmatia was of Slavic ancestry, which arrived from the area somewhere in Poland probably along the direct route Nitra-Zalaszabar-Nin, and gradually expanded into the continental hinterland of Bosnia and Herzegovina by the 10th century, however, by the end of the 11th century did not in Eastern Slavonia. The 2015 study of medieval skeletal remains in Šopot (14th-15th century) and Ostrovica (9th century) found out they cluster with other Dalmatian sites as well Polish sites, concluding that "PCA showed that all Eastern Adriatic coast sites were closely related in cranial morphology, and thus, most likely had similar biological makeup".