An article named "The Enigmatic Russian Soul" spits out the bare truth on Slavic origins:
A number of similar myths exist. For example, the common legend of an ancient Slavic culture. There never was, and could not be, such a concept because the term “Slavs” in all Western European languages always referred simply to “slaves” -- the pagan people who survived under the oppressive regimes of one conqueror after another.
My guess is that there's a distinction between "serf" and "slave," with the former being bonded to an estate and the latter general property because they were too individualistic to work with the order of a civilization despite needing it. When Europe grew, it shed people to the middle east and to Eurasia (sometimes called "Eastern Europe") who were not necessary for its growth, were criminal or had other problems working with others.
5,000 years later and self-governance is still a problem. Demography is destiny.