West Slavs
According to 2013 autosomal IBD survey "of recent genealogical ancestry over the past 3,000 years at a continental scale", the speakers of Serbo-Croatian language share a very high number of common ancestors dated to the migration period approximately 1,500 years ago with Poland and Romania-Bulgaria cluster among others in Eastern Europe. It is concluded to be caused by the Hunnic and Slavic expansion, which was a "relatively small population that expanded over a large geographic area", particularly "the expansion of the Slavic populations into regions of low population density beginning in the sixth century" and that it is "highly coincident with the modern distribution of Slavic languages". The 2015 IBD analysis found that the South Slavs have lower proximity to Greeks than with East Slavs and West Slavs, and "even patterns of IBD sharing among East-West Slavs–'inter-Slavic' populations (Hungarians, Romanians and Gagauz)–and South Slavs, i.e. across an area of assumed historic movements of people including Slavs". The slight peak of shared IBD segments between South and East-West Slavs suggests a shared "Slavonic-time ancestry". The 2014 IBD analysis comparison of Western Balkan and Middle Eastern populations found negligible gene flow between 16th and 19th century during the Islamization of the Balkans.