In 1857, the Supreme Court ruled in Dred Scott v. Sanford that the enslaved Scott's four year residence in the free North was not sufficient to make him a free man. In his majority opinion, Chief Justice Roger B. Taney cited two main rationales for ruling against Scott; first, as an African American, Scott "had no rights which the white man was bound to respect," and was therefore not eligible bring a suit to court. Second, slaves were property, the same as any other, so by prohibiting slavery north of the 36'30? line, the Missouri Compromise of 1820 violated citizens' constitutional rights against unwarranted seizure of property. Taney's decision effectively made it impossible to prevent the spread of slavery, even in states that had outlawed it decades earlier. To this day, many legal historians consider the Dred Scott ruling the worst decision ever made by the Supreme Court; it was overturned by the passage of the 13th and 14th amendments to the Constitution in 1865 and 1868, respectively.
The question is simply this: Can a negro, whose ancestors were imported into this country, and sold as slaves, become a member of the political community formed and brought into existence by the Constitution of the United States, and as such become entitled to all the rights, and privileges, and immunities, guarantied by that instrument to the citizen? One of which rights is the privilege of suing in a court of the United States in the cases specified in the Constitution....
We think [people of African ancestry] are not, and that they are not included, and were not intended to be included, under the word "citizens" in the Constitution, and can therefore claim none of the rights and privileges which that instrument provides for and secures to citizens of the United States…
They had for more than a century before been regarded as beings of an inferior order, and altogether unfit to associate with the white race, either in social or political relations; and so far inferior, that they had no rights which the white man was bound to respect; and that the negro might justly and lawfully be reduced to slavery. . . . He was bought and sold, and treated as an ordinary article of merchandise and traffic, whenever a profit could be made by it. This opinion was at that time fixed and universal in the civilized portion of the white race.
For if they were so received, and entitled to the privileges and immunities of citizens, it would exempt them from the operation of the special laws and from the police regulations which they considered to be necessary for their own safety. It would give to persons of the negro race, who were recognized as citizens in any one State of the Union, the right to enter every other State whenever they pleased, singly or in companies, without pass or passport, and without obstruction, to sojourn there as long as they pleased, to go where they pleased at every hour of the day or night without molestation, unless they committed some violation of law for which a white man would be punished; and it would give them the full liberty of speech in public and in private upon all subjects upon which its own citizens might speak; to hold public meetings upon political affairs, and to keep and carry arms wherever they went. And all of this would be done in the face of the subject race of the same color, both free and slaves, and inevitably producing discontent and insubordination among them, and endangering the peace and safety of the State.
The act of Congress, upon which the plaintiff relies, declares that slavery and involuntary servitude, except as a punishment for crime, shall be forever prohibited in all that part of the territory ceded by France, under the name of Louisiana, which lies northand not included within the limits of Missouri. And the difficulty which meets us at the threshold of this part of the inquiry is, whether Congress was authorized to pass this law under any of the powers granted to it by the Constitution; for if the authority is not given by that instrument, it is the duty of this court to declare it void and inoperative, and incapable of conferring freedom upon any one who is held as a slave under the laws of any one of the States.
The power to expand the territory of the United States by the admission of new states is plainly given. But the power of Congress over the person or property of a citizen [is] regulated and plainly defined by the Constitution itself. And when the Territory becomes a part of the United States, the Federal Government enters upon it with its powers over the citizen strictly defined, and limited by the Constitution.It has no power of any kind beyond it; and it cannot, when it enters a Territory of the United States, put off its character, and assume discretionary or despotic powers which the Constitution has denied to it.
. . . [T]he rights of private property have been guarded with . . . care. Thus the rights of property are united with the rights of person, and placed on the same ground by the fifth amendment to the Constitution, which provides that no person shall be deprived of life, liberty, and property, without due process of law. And an act of Congress which deprives a citizen of the United States of his liberty or property, merely because he came himself or brought his property into a particular Territory of the United States, and who had committed no offence against the laws, could hardly be dignified with the name of due process of law.
Upon these considerations, it is the opinion of the court that the act of Congress which prohibited a citizen from holding and owning property of this kind in the territory of the United States north of the line therein mentioned, is not warranted by the Constitution, and is therefore void; and that neither Dred Scott himself, nor any of his family, were made free by being carried into this territory; even if they had been carried there by the owner, with the intention of becoming a permanent resident.
Source: Paul Fink, Dred Scott V. Sandford: A Brief History with Documents (Boston: Bedford, 1997). Full text available at http://www.law.cornell.edu/supct/html/historics/USSC_CR_0060_0393_ZO.html