Slavery was a part of the larger issue called "States Rights", as given under the 9th and 10th Amendments to the Constitution. All powers not specifically given to the Federal Government by the Constitution (and there were very few of those) was given to the States. This even included those rights and powers that there NOT mentioned in the constitution.

Slavery was a right given to individuals under the Constitution in 1787. It was the States that had the power to abolish it on a State by State basis. Contrary to public perception that right was not placed in the Constitution for the benefit of the southern states. It only required the ratification of only 9 of the 13 states to accept the NEW Constitution. None of the 4 Southern States were necessary to ratify that Constitution. However one State was extremely important to the new nation being formed by the New Constitution, NEW YORK.

No matter how many of the State that ratified that Constitution, Without the State of New York Ratifing the New Constitution the new nation would have been split into two parts. New York did now Ratify the Constitution until well after the new Nation was formed. It was also one of the largest slave holding states in 1787 because they were used to work the docks in New York city Harbor.

Anyway that slavery Cause in article 4 had to be repealed by the 13th Amendment. Abraham Lincoln owned his wifes Slaves longer than Robert E. Lee did. Abraham Lincoln did not bring his wifes slaves to Washington D.C. because under an 1850 District of Columbia law he would have had to have freed them. Abraham Lincoln supported a federal Law for Kentucky which protected the slave owners of that state who were loyal to the Union like his father-in-law.

With all that said the Southern people of 1860, because of the intent of John Brown's raid to arm slaves in Virginia in rebellion, felt that the Abolishionist, backed by the Northern States and the Federal Government occupation of State armouries (which the southern people saw as a direct threat because of John Brown) is what pushed the southern states to make slavery the issue it became in responce to what they saw as a direct threat of instigation of a slave rebellion. Which is what the Emancipation Proclaimation and the raising of the United States Colored Troops regiments confirmed this to the southern people.