The demographic transition is a theory that sought to explain demographic, originally, the relationship between demographic change and socio-economic changes that took place in the eighteenth century in the developed countries of Europe and thus the relationship between population, development and population growth. The demographic transition explain the shift from a preindustrial demographic regime, leaded by head rates of mortality and birth to another industry with strong population growth and subsequently postindustrial, with very low rates of death and birth.
There are four phases of demographic transition: 1. The first stage, typical of pre-industrial societies, birth rates and death rates are too high, so the natural increase of the population is slow. This stage is the one that marked the history of humanity from its origins to the eighteenth century. In the Middle Ages and the Modern ages birth and mortality rates were close to 50%. In this phase, many children were born while at the same time. Mortality was very high even in years of ordinary life by the insecurity, poor nutrition, hygiene, sanitation, etc. Even more in the years of catastrophic mortality caused by war,