Economists Reinvent the Wheel

Brad DeLong is an interesting guy, a former Clinton bureaucrat, an economics professor, and prolific blogger. He posts a handout for an economic history class to be given this fall. There's lots of formulas and logic, but I'll excerpt the two key pieces:

The Puzzle:

"In the context of Economics 113—American Economic History—we have a
definite puzzle: it was Britain that was ahead in technology and was where
technology was moving ahead the fastest in the first half of the nineteenth
century, and yet it was America that appears to have had the fastest perperson
economic growth. According to eh.net, British growth in real GDP
per capita averaged 0.50% per year in the first half of the nineteenth
century; American real GDP per capita growth averaged 0.86% per year
from 1790-1850.1"

The Conclusion:

The westward expansion—the Erie Canal, the steamboats, expulsion of
Indians from the near midwest and the inland southeast, et cetera—thus
looks absolutely key to the form that economic growth took in pre-Civil
War America.

(The reasoning involves looking at capital, natural resources, level of technology, and labor.)

Seems to be that was Turner's "frontier hypothesis" of American history.