Wrong question. What law gave the Government power to deprive them of their right?
A right which was supported by the Fourth Amendment and by the due process and just compensation clauses of the Fifth Amendment.
Slaves, no matter what people think of the idea now, were legal property, and the Congress could no more deprive these settlers of their property than they could deprive them of their firearms or their tools.
We're not talking about a legislature invading people's Ninth Amendment rights with due process and proper legislation written for compelling public purposes. We're talking uncompensated and systematic deprivation of real and/or personal property which could not be taken without an amendment to the Constitution (as, for example, the Eighteenth Amendment, which was required before the Government could declare the possession of alcohol illegal).
Due process would have required an amendment to the Constitution to exclude slaves from the Territories. There was no due process, even under Douglas's Kansas-Nebraska Act, which was only a statute.
The Constitution. Article III, Section 3. "The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States; and nothing in this Constitution shall be so construed as to Prejudice any Claims of the United States, or of any particular State."
A right which was supported by the Fourth Amendment and by the due process and just compensation clauses of the Fifth Amendment.
Completely irrelevant. Congress was not depriving the slave-owner of his slave. He was free to reside in any state in the Union which allowed slavery. He was free to move to any terriitory he wanted. He was not, however, free to take his chattel with him if Congress passed a law preventing it, any more than he was free to take his chattel into any state if that state had passed a law preventing it.
We're talking uncompensated and systematic deprivation of real and/or personal property which could not be taken without an amendment to the Constitution (as, for example, the Eighteenth Amendment, which was required before the Government could declare the possession of alcohol illegal).
Nonsense. Congress was depriving them of no property, Congress was seizing nothing. Congress may not have had the power to interfere with the ownership of slaves in the individual states but the Constitution clearly gave Congress the right to legislate activities in the territories. And since there wasn't any explicit Constitutional protection for slavery then there was nothing that prevented Congress from outlawing in territories under their legislative jurisdiction.