Although there can be more than one kind of demographic transition, the most commonly used meaning is for one from higher to lower birth rates. Frequently this transition is described in four states.
The first, or pre-modern stage was the state of the world for most of history. This stage is characterized by high birth rates and generally high but variable death rates. Population growth was slow and governed by the death rate due to pestilence, famine, war and a simple lack of knowledge if disease prevention.
The first change occurred in Western Europe near the end of the 18th century. This time period coincided with industrialization and urbanization. A number of factors including a stabilization of the food supply were in play. Agriculture itself underwent a revolution in understanding like plant breeding, crop rotation, etc. Also important was the advent of new staples such as potatoes and corn. Equally important was the scientific understanding of disease mechanisms. Clean water and sewer systems along with personal hygiene went a long way to lower death rates. During this second stage, birth rates rose while death rates fell, hence more rapid population growth.
Stage three is characterized by a beginning of the fall of birth rates. Again this was first seen in Western Europe, around the end of the 19th century. As society urbanized the need for and actual cost of children changed. Parents saw that a large number of births were no longer necessary to ensure help on the farm and in old age. Child labor laws in urban areas, and the increasing importance of education meant children were also more expensive in the setting of a nuclear family. By the middle of the 20th-century convenient contraceptive technology greatly improved family planning.
The fourth stage is characterized by stability. Birth rates for all the aforementioned reasons are down. Death rates are down due largely to nutrition and health care practices, especially vaccinations. This is the hallmark of the developed world where low birth and death rates greatly moderate population growth and the age distribution shifts to an older average age. The single most important factor, across all cultures, is the education of women. When women are educated they are empowered to seek an independent income and make independent decisions about their family status.
The decrease in the United States has been so successful that the birth rate is now below the replacement rate. When fertility falls below 2.1 births per female, population decline is inevitable. In the US this has been the case for almost 50 years now. So why aren’t we losing population? Migration.
This migration to the United States comes from all over the world but is most obvious among Mexican and Central American populations. People of Hispanic origin, be they citizens or more recent immigrants of variable status represented just over seven percent of the population in 2000. Currently they represent almost seventeen percent.
Whites, which have dominated all aspects of American society have already reached minority/majority status (non-Hispanic whites are outnumbered by all others) in several south and western states. It is predicted that by about 2040 whites will only account for a plurality of citizens.
The takeaway here is that immigration is essential to our survival and if current trends continue our country will be a lot “browner” in the future. This is causing unease and even fear among the diminishing white population.