There is legitimate self-interest and mercenary self-interest. The latter is not a good reason to start a war.
For Diogenes, it's always about mercenary self-interest for the North. He never examines Southern motives closely enough to see the mercenary component.
Remember, it hadn't been that long since New York, New Jersey, New Hampshire, Connecticut, Pennsylvania, Massachusetts, Rhode Island, Delaware, and Maryland had voted to enshrine slavery in the U.S. constitution.
I'm not sure what theat has to do with anything, but what "enshrine"? They accepted the status quo and gave South Carolina and Georgia the guarantees they wanted.
And actually, it had been a long time. Consider what the US was like in your grandfather's day and what it is today.
Legitimate self-interest is what we do. Mercenary self-interest is what our opponents do.
That is not a very sophisticated distinction but that's seems to be how we think.
And consider what Kasper Gutman told Sam Spade in the “Maltese Falcon”:
“That's an attitude, sir, that calls for the most delicate judgment on both sides. Because, as you know, sir, in the heat of action men are likely to forget where their best interests lie and let their emotions carry them away.”
” . . . in the heat of action men are likely to forget where their best interests lie . . .”
Today is the 154th anniversary of the third day of the battle of Gettysburg. Casualties (dead, wounded, and missing) an estimated 50,000.
I salute the courage and sacrifice of the men on both sides.