Below are five maps which attempt to show the linguistic territories of the main divisions of the Indo-European language family around 3000 BC, 2500 BC, 2000 BC, 1500 BC and 1000 BC.
Please note that the extents of these linguistic territories are largely speculative. Also note that these linguistic territories do not necessarily correspond with the territories of identifiable archaeological cultures.
In my view, the Proto-Indo-European language existed before 5000 BC in the forested areas west of the Ural Mountains. This Proto-Indo-European language split into two dialects as it expanded southwards into the steppe zone sometime around 5000 BC. I call these two dialects North Indo-European (or Forest Indo-European) and South Indo-European (or Steppe Indo-European).
In red is the linguistic territory of North Indo-European (or Forest Indo-European). The descendants of North Indo-European are Balto-Slavic and Indo-Iranian. In my view, the Cimmerian and Daco-Thracian languages were southern extensions of the Balto-Slavic group, while the Scythian language of course belongs to the Indo-Iranian group.
In the last two maps below (1500 BC & 1000 BC), the Indo-Iranian dialect of North Indo-European (in pink) is distinguished from the Balto-Slavic dialect (in red).
In yellow is the linguistic territory of South Indo-European (or Steppe Indo-European). The descendants of South Indo-European are Celtic (including Celtoid), Italo-Illyric, Greco-Phrygian and Tocharian. This last group was an early offshoot from South Indo-European and soon diverged greatly from it; for this reason, a light green color is used for Tocharian on the four maps after the first one.
[February 16, 2022 – I have recently come to believe that Illyric was neither part of an Italo-Illyric branch, nor even part of the larger grouping that I define here as South Indo-European – see https://vellaunos.ca/2022/01/30/illyrians-and-albanians/ ]
It is my opinion that the Yamnaya Culture and its predecessors were not speakers of a unified Proto-Indo-European language. The language of the Yamnaya Culture was the southern dialect of Proto-Indo-European from which the Celtic, Italo-Illyric and Greco-Phrygian languages developed.
As for the northern dialect of Proto-Indo-European, this was probably the language of the Comb Ceramic (or Pit-Comb Ware) Culture. It was also the language of the Corded Ware Culture and of its easterly extensions (Middle Dnieper, Fatyanovo-Balanovo).
In brown is the linguistic territory of Anatolian, which in my view is the result of the (partial) adoption of South Indo-European by the non-Indo-European speakers north of the Caucasus who had produced the Maykop Culture.
In beige is the territory of the language that became Greek and Phrygian. This language in my view resulted from a fusion of the eastern dialect of North Indo-European (i.e. Pre-Proto-Indo-Iranian) with the South Indo-European language that was still spoken on the Pontic Steppe after the Yamnaya period. (This would have occurred before the centum-satem split.)
(Armenian is probably an offshoot of this language group, moving southwards over the Caucasus into historic Armenian territory while Greco-Phrygian moved westwards through the Pontic steppe.)
In the last two maps below (1500 BC & 1000 BC), the dialectal division between Italo-Illyric (in yellow) and Celtic (in light orange) is shown.
In orange is the linguistic territory of Germanic, which in my view is the result of a fusion of North Indo-European (particularly Pre-Proto-Baltic) and South Indo-European (particularly Pre-Proto-Celtic).
I have created a cladogram of the Indo-European language family: https://vellaunos.ca/2021/03/24/a-cladogram-of-the-indo-european-language-groups/