Population changes are influenced by four major factors. The birth rate (the number of births per 1,000 people) and the death rate (the number of deaths per 1,000 people) are fundamental in determining natural population growth. Immigration refers to people moving into a country, while emigration refers to people leaving a country. These components together influence the overall population size and structure, as well as the growth rate in a given region. These four factors are key in understanding population dynamics and their social and economic impacts.