Sorry Doyle I failed to mention the author of the book:

William Rawle, who was appointed United States attorney for Pennsylvania in 1791 by George Washington, wrote an important study on United States government. His book was in use at West Point when men such as Robert E. Lee attended the U. S. military academy. The Rawle's textbook says this about secession: "The secession of a state from the union depends on the will of the people of such state." He adds, "It depends on the State itself whether it will continue a member of the Union. To deny this right, would be inconsistent with the principles on which all our political systems are founded; which is, the people have, in all cases, a right to determine how they will be governed." Rawle does not treat secession lightly; he says "To withdraw from the union is a solemn and serious act", yet states retain the right to do so.