After national languages, the most intensively studied area of Slavic sociolinguistics is dialectology. Investigations into the dialectology of the major Slavic languages were begun over a century ago, and all the modern Slavic languages are now provided with dialect descriptions, sometimes based on extensive surveys. The material gathered has concentrated on variation in phonetics, morphology and vocabulary. Work on dialectology has tended to be biased toward the national languages, so that dialects have usually been seen as regional variants of individual languages, as dialect clusters related centripetally to national standard variants, rather than as part of a total continuous trans-national dialect map of Slavic.
The Slavic languages in Europe – in other words, excluding non-European Russia – show the densely packed dialect map familiar in European languages. After the settlement of the Slavs in their present homelands, which was substantially completed by about the sixth century ad, the settled, agricultural lifestyle of the Slavs tended to discourage geographical mobility. The effects of military and cultural activity and dominance were felt more by the urban classes than by the rural population. It was only in the twentieth century that rural populations began to achieve significant geographical mobility. The two World Wars, and the aftermath of the Russian Revolution, played an important role in this social change, both directly and indirectly, as whole areas of the rural population in the USSR perished or were relocated.