The "Demographic Transition" is a model that describes population change over time. It is based on an interpretation begun in 1929 by the American demographer Warren Thompson, of the observed changes, or transitions, in birth and death rates in industrialized societies over the past two hundred years or so.
By "model" we mean that it is an idealized, composite picture of population change in these countries. The model is a generalization that applies to these countries as a group and may not accurately describe all individual cases. Whether or not it applies to less developed societies today remains to be seen.
Answer:
Many things, such as weather change, migration cycles being thrown off, droughts, floods, and more
It's a geographic region in Africa that is the climatic division between the Sahara Desert and the African Savannah.
