Slavery is to be condemned in the Declaration of Independence
Thomas Jefferson was the great fighter against slavery in the emerging republic. He tried to combat it with his logic, and he wanted it condemned in the Declaration of Independence. His draft blamed George III for slavery in the colonies, but this was not accepted by the Continental Congress. Virginia had passed laws against the importation of slaves and these have been vetoed by the British Government, hence Jefferson’s resentment.

In his Memoir
He explained in his Memoir concerning the Declaration: ”The clause…reprobating the enslaving the inhabitants of Africa, was struck out in complaisance to South Carolina and Georgia, who had never attempted to restrain the importation of slaves, and who, on the contrary, still wished to continue it. Our northern brethren also, I believe, felt a little tender under those censures; for although their people had very few slaves themselves, yet they had been pretty considerable carriers of them to others.”
Law enacted in 1793
A law governing the return of fugitive slaves had been enacted in 1793, based on Sec. 2, Art.IV of the Constitution, which provided that a person ”held to service or labor” under the laws of one state and escaping to another should be returned to the person to whom he was obligated. This applied also to indentured servants.
Jefferson’s relentless fight against slavery
Jefferson fought slavery relentlessly. In 1784 the Continental Congress appointed him chairman of a committee to draft a plan of administration for territories in the north of 31° N. Lat., including land later admitted as the states of Alabama, Mississippi, Tennessee, and Kentucky. On March 1, 1784, Jefferson made a report that included the provision that ”after the year 1800 of the Christian era there shall be nether slavery nor involuntary servitude in any of the said states.” this clause was rejected by the majority of one vote, causing Jefferson to write: ”The voice of a single individual… would have prevented this abominable crime from spreading itself over the new country. Thus we see the faith of millions unborn hanging on the tongue of one man, and heaven was silent in that awful moment!”

The Famous Northwest Ordinance
The Continental Congress on July 13,1787, adopted the famous Northwest Ordinance (An ordinance for the Government of the Territory of the United States Northwest of the River Ohio). This stipulated that ”there shall be neither slavery nor involuntary servitude in the said territory.” This ordinance was re-adopted under the Constitution, August 7, 1789. The same prohibition of slavery was incorporated by Congress in acts creating the governments of territories of Indiana, 1800, Michigan, 1805, Illinois,1809, Wisconsin, 1836, and Iowa,1838.

The New Federal Government
But when North Carolina in December, 1789, ceded its western lands to the new federal government, it stipulated that ”no regulations made or to be made by Congress shall tend to emancipate slaves.” Congress accepted the condition in its act for the government of the territory south of the Ohio, and similarly kept its hands off when creating new southern states. Five territorial acts from 1798 to 1822 either accepted or made no provision concerning slaver. By 1846 six southern states in which slavery was permitted had been admitted without any prohibition against slavery: Tennessee,Louisiana, Mississippi, Alabama, Arkansas, and Florida, and a seventh, Missouri, had tricked Congress by accepting restrictions in order to acquire statehood, and then spurning them.

Prohibition of Slave trade
The slave trade was prohibited in 1808 and slavers became subject to seizure when caught, but they still managed to deliver their cargoes. A number of African sloops of war were on patrol of the African West Coast for decades before the Civil War. The USS San Jacinto was returning from such a patrol when it Captured the Confederate commissioners Mason and Slidell.