Supplementary to this grand act was the Constitutional prohibition of the African slave-trade after the year 1808.

Together they were intended to discourage the growth of slavery--the first by restricting its territorial extension, the second, by arresting its numerical increase.
And without doubt they would have placed the evil in the way of ultimate extinction had other and far reaching causes not intervened to produce adverse social and political conditions.
The first of these causes, in point of time, were certain labor-saving inventions in England, which vastly enhanced the demand for raw cotton.
Arkwright's invention of the spinning machine about twenty years prior to the adoption of the Constitution, perfected by the spinning-jenny of Hargreaves, and the mule of Crompton, "turned Lancashire," the historian Green says, "into a hive of industry." The then rapid demand for cotton operated in time as a stimulus to its production in America.

Increased productivity raised the value of slave property and slave soil.

But the slow and tedious hand method of separating the fiber of the cotton bulb from the seed greatly limited the ability of the Cotton States to meet and satisfy the fast growing demand of the English manufacturers, until Eli Whitney, in 1793, by an ingenious invention solved the problem of supply for these States.

The cotton gin was not long in proving itself the other half--the other hand of the spinning machine.
From that year the slave interests of the South rose in market value, and its industrial system assumed unexpected importance in the economic world.