When you initiate an aggressive course of open and armed conflict, one you have every intention of winning then you must assume that your opponent will come at you with every thing he's got and you, the aggressor will be invaded and occupied when the fortunes of war turn against you, the aggressor. Just as the Confederacy did in June/July 1863 when it moved aggressively into Maryland and then on into Pennsylvania. They were the aggressor. And they got their butts kicked. The South bought this on themselves. And so Professor let me ask you something: If the South had won it's war of aggression against the Union would it have continued the system of slavery or would it have ended it? What say you , Reb?
Yes it was.
There is no constitutional right to secede,
There is, but for a better understanding, see "Declaration of Independence."
enslaving an entire race made a mockery of our stated intention to be a nation of free people,
The people didn't really care about that until the South decided to leave with their money. Also, the North was still keeping slaves as well.
of all races and the Confederacy opened hostilities by firing on Ft. Sumter.
Lincoln initiated hostilities by sending a fleet of warships and giving them orders to attack the Confederates.
And that's if you ignore the fact that Major Anderson initiated hostilities by seizing unfinished Fort Sumter in the dead of night while people were sleeping.