Interregional slave trade
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The interregional slave trade was the trade of slaves within the United States that reallocated slaves across states during the antebellum period. The direction of this trade occurred primarily from states of the Old South (Georgia, Maryland, Delaware, Virginia, Tennessee, Kentucky, South Carolina, North Carolina, and the District of Columbia) to states of the Deep South and the West Territories (Texas, Louisiana, Mississippi, Alabama, Arkansas, Florida). Transactions in the interregional slave market were driven primarily by interregional differences in the marginal productivity of labor, which were given by the relative advantage between climates for the production of staple goods. This disparity in productivity created arbitrage opportunities for traders to exploit and ultimately facilitated regional specialization in labor production. Due to a lack of data, particularly with regard to slave prices, land values, and export totals for slaves, the true effects of the interregional slave trade on both the economy of the Old South and general migration patterns of slaves into southwestward territories remain uncertain and have served as points of contention among economic historians.
Economics of the interregional slave trade 
The internal slave trade among states emerged in 1760 as a source of labor in early America. Along with other factors, the abolition of transatlantic slave trade in 1809 placed increased importance on the role of this interregional trade. It is estimated that between 1790 and 1860 approximately 835,000 slaves were imported to the American South. However, analysis by Robert Fogel and Stanley Engelman suggests that only 16 percent of the total migration of slaves was due to sale of slaves through domestic trade.
The biggest sources for the domestic slave trade came from exporting states in the Upper South such as Virginia, North Carolina, Maryland, and Kentucky. From these states most slaves were imported into South Carolina, Georgia, Alabama, Mississippi, Louisiana, and Arkansas. Fogel and Engelman attribute the larger proportion of interregional slave migration (i.e. migration not due to slave trade) to movement as whole plantations with slave owners.
Contributors to the growth of interregional slave trade 
Historians who argue in favor of soil exhaustion as an explanation for slave importation into the Deep South posit that exporting states emerged as slave producers because of the transformation of agriculture in the upper south and the increased demand for labor in the Deep South due to the success of sugar and cotton crops. Because of the deterioration of soil and an increase in demand for food products, states in the upper south shifted crop emphasis from tobacco to grain which required less slave labor. This decreased demand left states in the Upper South with an excess supply of labor.
At the same time, the invention of the cotton gin in the late 18th century transformed cotton into a profitable crop that could be grown inland in the Deep South. The consequent boom in the cotton industry coupled with the labor intensive nature of the crop created a need for slave labor in the Deep South that could be satisfied by excess supply further north.
The increased demand for labor in the Deep South pushed up the price of slaves in places like New Orleans. This created price differences between the Upper and Deep South. As a result, slave traders took advantage of this arbitrage opportunity by buying at lower prices in the Upper South and then sold slaves for a profit after transporting them further south. In addition, we can see the rising prevalence of “breeding” slaves for export in the Upper South where reproductive ability of women was advertised as selling point and a feature that increased value.
Although not as significant as the exportation of slaves to Deep South, the rising practice of using slaves as a cash substitute by farmers and land owners who needed to pay off loans contributed to the growth of the internal slave trade.
Estimates of slave prices, trader income, and alternative labor comparisons 
Using an admittedly limited set of data from Ulrich Phillips (includes market data from Richmond, Charleston, mid-Georgia, and Louisiana), Robert Evans, Jr. estimates that the average differential between slave prices in the Upper South and Deep South markets from 1830-1835 was $232. Although this differential only deals with price and doesn’t account for transport costs and other operating costs (e.g. clothing, medical costs), the price gap displays a potential arbitrage opportunity (assuming costs were low enough).
In fact, Evans suggests that interstate slave traders received a wage greater than that of an alternative profession in skilled mechanical trades. If skilled mechanical trades can be considered a reasonable alternative occupation for slave traders, then it appears that interregional slave traders are made better off, at least in monetary terms.
However, if slave traders possessed skills similar to those used in supervisory mechanics (e.g. skills used by a chief engineer), then slave traders received an income that was not greater than the one they would have received had they entered in an alternative profession. Nevertheless, it can probably be assumed that this was not the case with the majority of slave traders; we can reasonably assume that most traders did not possess the skills of a railroad president or chief engineer.
Economic implications of the interregional slave trade on the Old South 
Irish economic theorist John Elliot Cairnes suggested in his work The Slave Power that the interregional slave trade was a major component in ensuring the economic vitality of the Old South. Many economic historians, however, have since refuted the validity of this point, and the general consensus now seems to support Professor William L. Miller’s claim that the interregional slave trade “did not provide the major part of the income of planters in the older states during any period.”
Support for this theory comes from the idea that the returns gained by traders from the sale’s price of slaves were offset by both the fall in the value of land that resulted from the subsequent decrease in the marginal productivity of land and the fall in the price of output, which occurred due to the increase in market size as given by westward expansion. Due to this intuition, the net effect of the interregional slave trade on the economy Old South was negligible, if not negative.
Impact of the interregional slave trade on westward migration 
The primary issue that faces such analysis is determining the westward migration of the interregional slave trade from that incidental to the relocation of a slave’s master.
Robert William Fogel and Stanley L. Engerman first gave this figure to be 16 percent in their work Time on the Cross. This estimate, however, has been met with severe criticism due to the extreme sensitivity of the linear function employed to gather this approximation. A more recent estimate, given by Jonathan B. Pritchett, has this figure at about 50 percent, or about 835,000 slaves total between 1790-1850.
It is worth noting that, even without the interregional slave trade, it is plausible that migration would have occurred naturally due to natural population pressures and the subsequent increase in land prices. Professor Miller therefore contends that, “it is even doubtful whether the interstate slave traffic made a net contribution to the westward flow of the population.”
The nature of the market 
While the argument has been made that the interregional slave trade was one that resulted in “superprofits” for traders, evidence given by Jonathan Pritchett suggests that there existed a significant number of firms engaged in the market, a relatively dense concentration of these firms, and low barriers to entry such that exporters were price-taking, profit-maximizers acting in a market that achieved a long-run competitive equilibrium.
Within this market, the demand for prime-aged slaves, given by the ages 15–30, accounted for 70 percent of the imported slave population. However, due to the fact that the ages of slaves were often unknown by the traders themselves, physical attributes such as height often dictated demand in order to minimize asymmetric information.
- "Domestic Slave Trade". In Motion.
- Pritchett, Jonathan B. (June 2001). "Quantitative Estimates of the United States Interregional Slave Trade, 1820-1860". The Journal of Economic History 61 (2): 467–475. doi:10.1017/S002205070102808X. JSTOR 2698028.
- Evans, Jr., Robert (April 1961). "Some Economic Aspects of the Domestic Slave Trade, 1830-1860". Southern Economic Journal 27 (4): 329–227. doi:10.2307/1055531. JSTOR 1055531.
- Freudenberger, Herman; Herman Freudenberger and Jonathan B. Pritchett (Winter 1991). "The Domestic United States Slave Trade: New Evidence". Journal of Interdisciplinary History 21 (3): 447–477. doi:10.2307/204955. JSTOR 204955.
- Deyle, Steven (Spring 1992). "The Irony of Liberty: Origins of the Domestic Slave Trade". Journal of the Early Republic 12 (1): 37–62. doi:10.2307/3123975. JSTOR 3123975.
- Pritchett, Jonathan B. (Summer 1997). "The Interregional Slave Trade and the Selection of Slaves for the New Orleans Market". Journal of Interdisciplinary History 28 (1): 57–85. doi:10.2307/206166. JSTOR 206166.
- Miller, William L. (April 1965). "A Note of the Importance of the Interstate Slave Trade of the Ante Bellum Southrade of". The Journal of Political Economy. 2 73 (2): 181–187. doi:10.1086/259008. JSTOR 1829535.
- Kotlikoff, Laurence J.; Sebastian Pinera (June 1977). "The Old South's Stake in the Inter-Regional Movement of Slaves, 1850–1860". The Journal of Economic History. 2 37 (2): 434–450. doi:10.1017/S002205070009700X. JSTOR 2118765.
- Carstensen, F.V.; S.E. Goodman (Autumn 1977). "Trouble on the Auction Block: Interregional Slave Sales and the Reliability of a Linear Equation". Journal of Interdisciplinary History. 2 8 (2): 315–318. doi:10.2307/202791. JSTOR 202791.