The concerns regarding "over-urbanization" in developing countries during the 1970s and 1980s were mainly focused on the simultaneous occurrence of rapid urban growth and high levels of unemployment. To understand these concerns, we can refer to the Harris-Todaro model.
The Harris-Todaro model suggests that in developing countries, rural areas often face limited employment opportunities, leading to a rural-urban migration. However, upon arrival in urban areas, migrants often struggle to find formal employment due to a shortage of jobs. This results in high levels of unemployment in urban areas.
One of the main concerns with this phenomenon is that the rapid urban growth often outpaces the creation of new job opportunities. This can lead to overcrowding, inadequate housing, strained infrastructure, and social issues in urban areas. The lack of employment opportunities also means that many individuals are unable to escape poverty, exacerbating income inequality.