Thracian is a eastern Indo-European language, which was spoken in the Balkans in ancient times but which had apparently extended also into southern Russia ( Jokl 1929:278-98).
The Thraco-Phrygian group had, in the view of Bonfante ( 1939-44), supported by Jakobson, lexical connections with Slavonic.
Archeologically, the conquests of the Iron Age Scyths and their immediate predecessors, the Kimmerians, might have been too transitory to account for the implanting of a new language.
The Late Bronze Age urnfield expansion hardly made a serious penetration of Thracian territory ( Childe 1950, map on p. 182). But in the neolithic this region was occupied by the Mound culture (Gumelnitsa) in Bulgaria ( Gaul 1948:79-207) and by the Tripolye culture in the western Ukraine and northern Romania, both of which were characterized by painted pottery.
Here there were connections both with the Vardar-Morava culture of the southern Balkans and with the simple Danubians farther west. The Vardar-Morava culture represented the beginning of the neolithic in its area, and agricultural settlements were sufficiently fixed to form tells.
So were those of the Mound culture in Bulgaria. But tells did not extend north of the mouths of the Danube. Beyond were the substantial Tripolye villages of large houses, which must have had a considerable degree of permanency.
The fate of these cultures is not altogether clear. According to Childe ( 1947:144; 1950:142) and Gimbutas, this area was conquered at the beginning of the Bronze Age by warlike pastoralists with different burial rites, dwellings, and pottery, some of which was cord marked. For Gimbutas, these conquerors came from the eastern Ukraine and the southern Russian steppe.
But according to Sulimirski ( 1945, 1950) an altered form of the Tripolye culture was, despite this conquest, the basic underlying culture of the Ukraine down to the coming of the Iron Age Scyths. Hence one could suggest that Thracian was connected either with the older agriculturalists of the neolithic in the Balkans or with these conquerors from the steppe.
In conclusion, one might say about these satem languages of eastern Europe that, unlike the centum group, they have less tangible connection with the urnfields and perhaps more association with the peoples of the Eurasian plain, whether steppe pastoralists or river valley farmers.
source:
Indo-European Languages and Archeology by Hugh Hencken