What caused westward expansion in the United States?

Western Expansion during the nineteenth century was an important determinant of geographic distribution and economic activity in the United States today. However, while explanations abound for why the migration occurred– from the low price of land to a pioneering spirit – little empirical work has been done to determine which specific market forces were the most important drivers.

Applying quantitative analysis to historical explanations, a new study by economist Guillaume Vandenbroucke of the University of Southern California finds that the price of land was significantly less important to Westward Expansion than population growth and technological innovation leading to a decrease in transportation costs.

From 1800 to 1900, the United States tripled in size, from less than one million square miles to more than three million square miles. The geographic distribution of population also shifted, from about seven percent living in the West to roughly 60 percent. To examine what forces were most directly responsible for the magnitude of this movement and land accumulation, Vandenbroucke takes into account such factors as the amount of land available in the Eastern United States, wage and productivity growth in the East, and improvements in technologies and transportation infrastructures.

To account for the range of variables and possible factors, Vandenbroucke determined a model in which each factor was held at a constant level while the others shifted at historical rates.

“The most important forces are population growth and the decrease in transportation costs,” Vandenbroucke said. “Population growth is mostly responsible for the investment in productive land – without it less than half of the land accumulated in 1900 would have been accumulated.”

Surprisingly, Vandenbroucke found that changes in productivity in the East had little effect on the Westward Expansion, relative to population growth and a decrease in transportation costs – as he explains, rising wages and productivity makes it easier to move, but it also makes it less pressing to move.

Instead, he finds that population growth and technological innovation worked in concert as the main driving factors of Western Expansion. Specifically, the decrease in transportation costs induced Western migration and the redistribution of the American population – without it only 30 percent of the population would have been in the West in 1900, compared to an actual historical figure of 60 percent. Land improvement technology, such as the use of barbed wire to cut down on the time needed to build a fence, had a small effect on the accumulation of land in the West.

Vandenbroucke’s findings, appearing in the current issue of International Economic Review, have important implications for how to understand current population patterns and international immigration to the United States.