The decades 1951-1981 are referred to as the period of population explosion in India, which was caused by a rapid fall in the mortality rate but a high fertility rate of population in the country. During this period, the population of India grew from 361 million in 1951 to 683 million in 1981. There was a growth of population by 322 million during this phase. This was the phase when both death rate as well as birth rate declined. The average annual growth rate was as high as 2.2 per cent. It is in this period, after the Independence, that development activity was introduced through a centralised planning process and the economy started showing up ensuring the improvement of the living condition of people at large. Consequently, there was a higher growth rate. Besides, increased international migration bringing in Tibetans, Bangladeshis, Nepalis and even people from Pakistan contributed to the high growth rate.