"Developments in transportation, rather than in manufacturing and agriculture, sparked American economic growth in the first half of the nineteenth century." is not accurate. While development in transportation played a fundamental role in America's growth, if it were not for developments in manufacturing and agriculture the new technology in transportation could not have successfully been completed. Without the raw materials, and the products which came out of the early US iron and steel industry, (which were all ultimately determined by the United States agricultural market), the transportation revolution could not have been carried out. Also, with the rapid growth of the agricultural markets, American economic growth boomed. All three factors, (transportation, agriculture and manufacturing) played an equal role in sparking the American economic growth in the first half of the nineteenth century.
The cotton gin was just one of the few reasons in which the American economy grew at a rapid pace.
Eli Whitney's intention in 1793 of the cotton gin, which separated raw cotton from seeds and other waste, caused the economy to boom, with the growth of southern farms. As the southern plantations who could keep up with this new boom in cotton got larger and larger, small farmers moved west. This migration of small farmers to the west caused a need for developments in transportation to link the nation. In turn, these developments in transportation caused a boom in economy. Therefore, both manufacturing inventions and transportation inventions caused the growth in economy.
New inventions and capital investment led to the creation of new industries and economic growth. As transportation improved, new markets continuously opened. The steamboat made river traffic faster and cheaper, but development of railroads had an even greater effect, opening up immense areas of new territory for development. These new developments just opened up entrepreneurs...