I believe VI century Serbs and Croats , from which evolved today nations of Croats , Serbs, Montenegrins , Bosniaks , part of Macedonians , were not at all Slavs but Sarmatians ( I presented evidence for such claimes in tread Sarmatians , Serbs , Croats and I2a2- or something like that ), while Slovenians were mainly Slavs - that perfectly fits with diferences in mthDNA . So there was not two diferent migrations of Slavs , but Slavic and Sarmathian migration