in 1818 increasing the rewards to informers. Another act in the following
year directed the President to employ armed vessels for police in both
African and American waters, and incidentally made provisions contemplating
the return of captured slaves to Africa. Finally Congress by an act of 1820
declared the maritime slave trade to be piracy.[33] Smuggling thereafter
diminished though it never completely ceased.

[Footnote 33: DuBois, _Suppression of the Slave Trade_, pp. 118-123.]

As to the dimensions of the illicit importations between 1808 and 1860,
conjectures have placed the gross as high as two hundred and seventy
thousand.[34] Most of the documents in the premises, however, bear palpable
marks of unreliability. It may suffice to say that these importations were
never great enough to affect the labor supply in appreciable degree. So far
as the general economic regime was concerned, the foreign slave trade was
effectually closed in 1808.

[Footnote 34: W.H. Collins, _The Domestic Slave Trade of the Southern
States_ (New York [1904], pp. 12-20). _See also_ W.E.B. DuBois,
"Enforcement of the Slave Trade Laws," in the American Historical
Association _Report_ for 1891, p. 173.]

At that time, however, there were already in the United States about one
million slaves to serve as a stock from which other millions were to be
born to replenish the plantations in the east and to aid in the peopling of
the west. These were ample to maintain a chronic racial problem, and had no
man invented a cotton gin their natural increase might well have glutted
the market for plantation labor. Had the African source been kept freely
open, the bringing of great numbers to meet the demand in prosperous times
would quite possibly have so burdened the country with surplus slaves in
subsequent periods of severe depression that slave prices would have fallen
virtually to zero, and the slaveholding community would have been driven
to emancipate them wholesale as a means of relieving the masters from the
burden of the slaves' support. The foes of slavery had long reckoned that
the abolition of the foreign trade would be a fatal blow to slavery
itself. The event exposed their fallacy. Thomas Clarkson expressed the
disappointment of the English abolitionists in a letter of 1830: "We
certainly have been deceived in our first expectations relative to the
fruit of our exertions. We supposed that when by the abolition of the slave
trade the planters