In the late 1960s, 1970s and early 1980s the growth of many cities in the more developed regions, particularly in Europe, slowed significantly. Some cities actually became smaller as improved transportation and communications enabled populations to disperse to surrounding smaller "ring cities" and suburbs. These developments, coupled with declining annual growth in megacities, including those in developing countries, suggested that a deconcentration of population would develop as a general trend.
Comparison of data from different decades and different regions, however, does not suggest a general pattern. There is no clear relationship, for example, between migration to cities and urban population density. The role of international migration in the recent revitalization of core city growth also needs to be better appreciated and analysed.
Some problems of large cities, particularly traffic congestion, rising housing and living costs and air and water pollution, intensify with city size; others with rising numbers of people living in poverty, while the incidence of crime and disease worsens with unequal development. This has led to speculation that the economic and social opportunities which draw people to cities will eventually be overwhelmed by the urban disamenities. The cities where growth has slowed, however, have not experienced dramatic shifts in the balance of advantages and disadvantages. And many cities continue to grow even though their disamenities are clearly intensifying.
Selective migration may become an increasingly important factor in population distribution. People with skills and resources can take advantage of new technologies allowing them to leave the denser cities and stand to gain the most by doing so; they will leave behind less economically viable social environments for the poorer populations that remain. But urban opinion polls indicate more people say they want to move away than actually do so. Better understanding is needed of what determines individual mobility and of how to facilitate movements with desirable consequences.
The pattern of forces supporting and countering trends towards population concentration is clearly complex. Many of these are affected by the general economic climate
and by local and national government policies. It is quite possible that economic, technological and social changes will result in recurrent cycles of urban concentration and deconcentration.