I'm afraid that you would have to explain that to the graduates of the U.S. Military Academy at West Point as well as most every Law school in the U.S. prior to 1860 as the primary text they studied with regard to law was BLACKSTONE'S COMMENTARIES: WITH NOTES OF REFERENCE, TO THE CONSTITUTION AND LAWS, OF THE FEDERAL GOVERNMENT OF THE UNITED STATES; AND OF THE COMMONWEALTH OF VIRGINIA. IN FIVE VOLUMES. WITH AN APPENDIX TO EACH VOLUME, CONTAINING SHORT TRACTS UPON SUCH SUBJECTS AS APPEARED NECESSARY TO FORM A CONNECTED VIEW OF THE LAWS OF VIRGINIA, AS A MEMBER OF THE FEDERAL UNION. BY ST. GEORGE TUCKER, PROFESSOR OF LAW, IN THE UNIVERSITY OF WILLIAM AND MARY, AND ONE OF THE JUDGES OF THE GENERAL COURT IN VIRGINIA. PHILADELPHIA: PUBLISHED BY WILLIAM YOUNG BIRCH, AND ABRAHAM SMALL, NO. 17, SOUTH SECOND-STREET. ROBERT CARR, PRINTER. 1803.
One of the reasons the American colonists fought the Revolution was for the right to establish their own set of laws. Blackstone was entitled to his opinion, but his opinion had no binding effect on US law. Had the southern states gone to court to assert their right to withdraw from the Union, it is more than likely they would have prevailed. However, they chose instead to fire on the US flag at Ft. Sumter and suffered the deserved consequences.