The Indo-European proto-language was spoken south of the Caucasian mountains in the Aras river valley extending to the Black and Caspian Seas and north of the Black sea in the area between the Danube and Volga Rivers by a collection of semi-nomadic clans and rural tribes which more or less were hunters and gatherers around 6000 - 4000 B.C.E. Scholars have determined the location based on an extensive reconstructed vocabulary of Proto Indo-European language, and the habitat it describes. Therefore Proto- Indo European is an artificial reconstructed language (PIE), which was constructed out of fossil words. .
The break up of the early Indo- European society started around 4000 B.C.E. because of migration accompanied with specialization. The most significant form of specialization was from the nomadic, hunting lifestyle into herders and farmers. Also a major part of the break up were sound- shifts that occurred when certain groups migrated into various areas and were forced to deal with a different climate and landscape. Looking at the geography of were the Indo- European languages are spoken today it is clear that there were two groups a western group and an eastern group. These divisions of P.I.E are referred to as Centum and Satem. The sound-shift that happened was the velar sound K in Centum shifted to sibilant S in Satem. Centum is Latin for one hundred whereas Satem is the Sanskrit version for one hundred. .
The so called eastern group (Satem Branch) probably migrated around the eastern slopes of the Caucasian Mountains toward the north. Migrates to the north were Slavic people, who probably are the descendants of herders and farmers, who stayed in the general area of the Indo- European homeland and late spread out to today's Slavic regions of Europe. Other parts of this eastern group migrated around the southern tip of the Caspian Sea the Aryans of Iran, Persia and India and the Balts migrated to the Danzig river delta around 2000 B.