Establishment of industries in the cities resulted in the accumulation of wealth. The property resulted in urban growth, because it attracted persons from nearby villages. The mass migration of persons to cities imposed following problems (i) Overcrowding, leading to the problems of rehabilitation, sanitation and sewage disposal. (ii) Transportation and associated traffic problems. (iii) Environmental pollution, generated by industrial activities and automobiles, (iv) Noise pollution, (v) Various socioeconomic and cultural changes and problems related to juvenile delinquency and crime. The urbanization has utilized most of our fertile agricultural land for houses, industries, factories, government offices, schools hospitals and for constructing roads etc. This resulted in transport and import of necessary materials from nearby places. All these problems are socio-economic and increasing day by day. The man’s hunger for accumulation of wealth and to’ become supreme has resulted in blind competition of weapons and atomic energy. At present a few men or even one man can destroy the whole human race.
Urbanisation has also disturbed the pre-existing balance in the biosphere and has resulted in the population of those natural resources and air and water which support the world biota and which man utilizes himself. According to Geologists, man is gradually threatening its existence by disturbing the nature in an unplanned way for his physical comforts.
Factors that affect population, its growth, distribution and density are called demographic factors. The population (mortality), scarcity of food etc. are the demographic factors controlling the overall pattern of population density. These interact with the environment factors and determine the biotic potential of the population.
A population in its exponential growth phase shows a very high rate population increase. But once it becomes stabilised, the rate of population increase declines. The theory pertaining to such a population is called the Theory of Demographic Transition. A human population has witnessed the same demographic transition which is still exhibited by some of the underdeveloped and developing countries. It must have passed through the following phases in sequence.
1. In the initial growth stage human population has very high birth and death rates prior to.modern era. This is still found in Afganistan and Angola.
2. High birth and death rate in 18th century which are still seen in Pakistan, Indonesia and Bolivia.
3. Nigh birth and moderate death rate in the 19 century exhibited by populations of present day developed countries when these were developing and is seen at present in the presently developing countries like India and Morocco.