I'm going to go waaaay out on a limb here and guess that what South Carolina was talking about was the Fugitive Slave laws. If I am correct in this then the charge is bogus and without merit. It is true that when the first fugitive slave acts were passed in the 1840's 1850 northern states enacted what wered Personal Liberty Laws to thwart it. They figured that by requiring jury trials, writs of habeas corpus, rights to legal representation, extradition requests and so forth the legal process could be used to keep the runaway slaves from being returned. The Supreme Court, not surprisingly, ruled in Prigg v Pennsylvania that such laws had to be enforced by the federal authorities but that state and local authorities could not be forced to act in fugitive slave cases. With the passage of the 1850 act, the states again responded with a round of personal liberty laws which were being challenged but per the earlier Supreme Court decision while the states could not hinder federal authorities in retrieving runaway slaves they did not have to assist.
So South Carolina's beef is that the norhern states were following Supreme Court guidelines.
Don't know.
It is asserted in this passage that compacts that were enumerated as early as the Declaration of Independence had been broken.
Some in the North recognized that the personal liberty laws were unconstitutional. I found the following in the Philadelphia Public Ledger of December 20, 1860:
THE CITIZENS OF MASSACHUSETTS AND THE PERSONAL LIBERTY BILLS
Chief Justice Shaw, B. R. Curtis, Joel Parker, and other citizens of Massachusetts equally distinguished, have addressed a letter to the people of that State on the Personal Liberty Bills, which they declare to be unconstitutional. They urge strongly the repeal of them and say:
We know it is doubted by some whether the present is an opportune moment to abrogate them. It is said -- We grant these laws are wrong, but will you repeal them under a threat? We answer no. We would do nothing under a threat. We would repeal them under our own love of right; under our own sense of sacredness of compacts; under our own convictions of the inestimable importance of social order and domestic peace; under our feeling of responsibility to the memory of our fathers and the welfare of our children, and not under any threat. We would not be prevented from repealing them by any conduct of others, if such repeal were in accordance with our own sense of right.
He who refuses to do a right thing meerly because he is threatened with evil consequences, acts in subjection to the threat. His false pride may enable him to disregard the threat, but he lacks the courage to dispise the wrong estimate of his own conduct, which conduct he knows would spring from his own love of duty. If every right-minded man must admit that he ought to govern his own conduct by these principles, are they applicable to the conduct of a great and populous State? On what ground can it be maintained that hundreds of thousands of innocent citizens are to be subjected to suffereing, because the false pride of their rulers refuses to do right? Mankind have been afflicted long enough and greviously enough by commotions and strifes and wars springing from such causes. We had hoped that the nature of our government would protect us from swelling the great sum of human misery, produced by the evil passions of rulers. We had hoped that, inasmuch as the masses of people can have no interest but to do right, they would have the discernment to perceive and the manlyness to do it, and would be too calm, too wise, too magnanimous intentionally to persevere in any wrong, and we hope so still.
But what is meant by the exhortation not to repeal these laws under a threat? Who threatens us if they should not be repealed?
Whatever may have been true in the past, whatever faults of speech and action may have been committed on the one side or the other, we firmly believe that the men from whom the worst consequences to our country and ourselves are likely to proceed, have no wish that these laws should be repealed, and no disposition to use any threats in reference to them. On the contrary, they desire to have them stand as conspicuous and palpable breaches of the national compact by ourselves; and as affording justification to themselves, to the world and to posterity, for the destruction of the most perfect and prosperous government which the Providence of God has ever permitted the wisdom of man to devise.