Recent research on the environmental setting of more than 3,000 Neolithic/Eneolithic sites, and of spatial distribution and shifts of various Eneolithic cultural groups, has revealed significant changes in the first half of the 4th millennium BC. A substantial reduction in traces of settlement activities and diminution of settlement territory is apparent. There is a shift from extremely good, but environmentally varied, conditions towards the uniform areas of the driest and warmest parts of the country with the finest Chernozem soils. These changes are obviously a reaction to robust climate change from long-term stable somewhat warm and dry conditions to a colder, wetter and shifting climatic regime. This idea has been supported by the R. A. Bryson Archaeoclimate Model which reveals decreasing temperatures, increasing precipitation and the changing regime of a year march of precipitation on a regional level around 5500 cal BP. A number of the subsequent changes in the subsistence strategies (particularly arable farming) and the settlement behaviour might be a reflection of the same change, however, cultural and social reasons for these changes cannot be excluded. Although there was a range of similar climate changes during the Holocene (supported by various proxy data as well as by the Archaeoclimate model) similar responses were not observed in the archaeological record of the later prehistoric periods.