On March 2, 1807, Congress passed “An Act to Prohibit the Importation of Slaves into any Port or Place Within the Jurisdiction of the United States, From and After the First Day of January, in the Year of our Lord One Thousand Eight Hundred and Eight.”

The bill provided that after January 1, 1808,

it shall not be lawful to import or bring into the United States or the territories thereof from any foreign kingdom, place, or country, any negro, mulatto, or person of colour, with intent to hold, sell, or dispose of such negro, mulatto, or person of colour, as a slave, or to be held to service or labour.

The first ship of African slaves arrived in North America at Jamestown, VA, in August 1619.

The slave trade was protected in the text of the United States Constitution in Article I, Section 9, Clause 1:

The Migration or Importation of such Persons as any of the States now existing shall think proper to admit, shall not be prohibited by the Congress prior to the Year one thousand eight hundred and eight, but a Tax or duty may be imposed on such Importation, not exceeding ten dollars for each Person.

With respect to amending this clause of the Constitution, Article V provides:

Provided that no Amendment which may be made prior to the Year One thousand eight hundred and eight shall in any Manner affect the first and fourth Clauses in the Ninth Section of the first Article; and that no State, without its Consent, shall be deprived of it’s equal Suffrage in the Senate.

In Federalist No. 42, Madison explained why these provisions were written into the Constitution:

It were doubtless to be wished that the power of prohibiting the importation of slaves, had not been postponed until the year 1808, or rather that it had been suffered to have immediate operation. But it is not difficult to account either for this restriction on the general government, or for the manner in which the whole clause is expressed. It ought to be considered as a great point gained in favor of humanity, that a period of twenty years may terminate for ever within these States, a traffic which has so long and so loudly upbraided the barbarism of modern policy; that within that period it will receive a considerable discouragement from the federal Government, and may be totally abolished by a concurrence of the few States which continue the unnatural traffic, in the prohibitory example which has been given by so great a majority of the Union. Happy would it be for the unfortunate Africans, if an equal prospect lay before them, of being redeemed from the oppressions of their European brethren! Attempts have been made to pervert this clause into an objection against the Constitution, by representing it on one side as a criminal toleration of an illicit practice, and on another, as calculated to prevent voluntary and beneficial emigrations from Europe to America. I mention these misconstructions, not with a view to give them an answer, for they deserve none; but as specimens of the manner and spirit in which some have thought fit to conduct their opposition to the proposed government.

Because of the provisions of the Constitution protecting the slave trade, the Three-Fifths Clause, and the Fugitive Slave Clause, Frederick Douglass said of the Constitution: “it was ‘conceived in sin, and shapen in iniquity.'” Douglass explained –

Had the Constitution dropped down from the blue overhanging sky, upon a land uncursed by slavery , and without an interpreter, although some difficulty might have occurred in applying its manifold provisions, yet so cunningly is it framed, that no one would have imagined that it recognized or sanctioned slavery. But having a terrestrial, and not a celestial origin, we find no difficulty in ascertaining its meaning in all the parts which we allege to relate to slavery. Slavery existed before the Constitution, in the very States by whom it was made and adopted. — Slaveholders took a large share in making it. It was made in view of the existence of slavery, and in a manner well calculated to aid and strengthen that heaven-daring crime.

America would have to fight a bloody Civil War before slavery was fully abolished via the 13th Amendment, reading –

Section 1.
Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.

Section 2.
Congress shall have power to enforce this article by appropriate legislation.