Many things, from economic collapse to AIDS, could prevent long-term fertility decline from taking hold in the poorest countries with the fastest population growth. In other, more fortunate, developing countries, fertility is falling rapidly, but past high fertility will fuel rapid population growth for some time to come. Globally, there are over a billion young people between 15 and 24, the parents of the next generation. With wise investment, they will power economic growth to support the other new generation, the growing numbers of older people. Immigrants are already changing the societies in which they live, especially in the urban areas.
Most countries lack the rich experience of the United States as a destination for immigrants.
Many fear the consequences of large-scale immigration, in the new economies as well as the mature ones, and it will not be easy to find good answers. But they do mean that policymakers at all levels in all countries have to consider their options very carefully. Today, all politics are international. The need for international co-operation in policymaking has never been greater. The second point for policymakers to remember is that immigration, urbanization and fertility levels are the result of decisions by individuals, not governments or economies.