Factors that can affect the size of a country's population are:
(i) Early marriage due to one reason or the other causes rapid population growth.
(ii) Changes in the birth rate may be due to the ability to have children and the desire to have a big family.
(iii) Owing to its respect for human life, Christianity discourages some practices like artificial birth control and abortion while some religious bodies like Islam do not discourage polygamy.
(iv) The use of modern medical facilities and establishment of bodies like the World Health Organisation have cut down the mortality rate.
(v) Immigration is the movement of people into a country. Some people go into a country for one reason or the other, and after staying for years, many nationalize while a good number of them marry and give birth there.
(vi) If death rate decreases, the population will increase.
(vii) If the number of women in a country is more than that of men, it is likely that the population of the country will increase.
(vii) Medical improvement increases the birth rate and decreases the death rate.