much
less than 40,000 slaves annually. From that time to about 1825 it
declined somewhat, but afterward increased enormously, so that by 1837
the American importation was estimated as high as 200,000 Negroes
annually. The total abolition of the African trade by American countries
then brought the traffic down to perhaps 30,000 in 1842. A large and
rapid increase of illicit traffic followed; so that by 1847 the
importation amounted to nearly 100,000 annually. One province of Brazil
is said to have received 173,000 in the years 1846-1849. In the decade
1850-1860 this activity in slave-trading continued, and reached very
large proportions.

The traffic thus carried on floated under the flags of France, Spain,
and Portugal, until about 1830; from 1830 to 1840 it began gradually to
assume the United States flag; by 1845, a large part of the trade was
under the stars and stripes; by 1850 fully one-half the trade, and in
the decade, 1850-1860 nearly all the traffic, found this flag its best
protection.[51]

72. ~The Quintuple Treaty, 1839-1842.~ In 1839 Pope Gregory XVI.
stigmatized the slave-trade "as utterly unworthy of the Christian name;"
and at the same time, although proscribed by the laws of every civilized
State, the trade was flourishing with pristine vigor. Great advantage
was given the traffic by the fact that the United States, for two
decades after the abortive attempt of 1824, refused to co-operate with
the rest of the civilized world, and allowed her flag to shelter and
protect the slave-trade. If a fully equipped slaver sailed from New
York, Havana, Rio Janeiro, or Liverpool, she had only to hoist the stars
and stripes in order to proceed unmolested on her piratical voyage; for
there was seldom a United States cruiser to be met with, and there were,
on the other hand, diplomats at Washington so jealous of the honor of
the flag that they would prostitute it to crime rather than allow an
English or a French cruiser in any way to interfere. Without doubt, the
contention of the United States as to England's pretensions to a Right
of Visit was technically correct. Nevertheless, it was clear that if the
slave-trade was to be suppressed, each nation must either zealously keep
her flag from fraudulent use, or, as a labor-saving device, depute to
others this duty for limited places and under special circumstances. A
failure of any one nation to do one of these two things meant that the
efforts of all other nations