If the rate of population growth of the United States between 1820 and 1850 had sustained over time, we'd have today approximately one and a half billion people in the United States.

如果在1820至1850年间,美国人口增长率保持下去的话,今天我们的美国,就会拥有近十五亿人口

耶鲁公开课 - 美国内战与重建课程节选