Many industrialized countries, such as Australia, Japan, the United States, and some European countries are at stage three. Meanwhile, most of the increase in world population can be attributed to the developing countries that have only reached stage two. When calculating a specific country's natural increase, additions or subtractions due to immigration are not included. Immigration Immigration to cities or across international borders is spurred by many factors. Environmental degradation due to population growth is one motivation to migrate.
Political unrest is another reason that people migrate.
Unemployment is one of the main reasons for immigration. In regions that lack economic opportunity people often seek employment in other countries where they perceive good jobs are plentiful. Today there are over 1 billion unemployed or underemployed people in the world. Growth Rate Natural increase combined with immigration equals the total population growth rate of a region. Most of the future population growth is projected to happen outside of the industrialized nations.