THE U.S. WESTWARD EXPANSION*
建立模型分析19世纪美国人口西迁和西部土地开发的关键驱动力，发现运输成本下降引发西迁，而人口增长推动土地投资。
The U.S. economic development in the 19th century was characterized by the westward movement of population and the accumulation of productive land in the West. This article presents a model of migration and land improvement to identify the quantitatively important forces driving these phenomena. The conclusion is that the decrease in transportation costs induced the westward migration, whereas population growth was responsible for the investment in productive land.