It is estimated that at least 83 countries and territories currently have fertility rates that are below the level needed to keep their population constant. Whereas most developed countries will experience a shortage of people as the century progresses, America is one of the few that may avoid demographic decline and maintain its share of world population.
移民太快会造成社会问题，但从长期看，移民增强了美国的实力。据估计，至少有83个国家和地区的生育率低于维持人口规模不降的必须生育率。随着21世纪的深入，大部分发达国家都将经历人口短缺，但美国是其中少数可能避免人口下降、维持其世界人口比例的国家之一。