People cared about ethics in war thats why. also wouldn't freeing the slaves ruin the whole point why the south fought i mean the seceded to keep slavery intact for generations to come.

In most lands where slavery was widespread, slavery was banned incrementally, and sometimes, there was no full ban on slavery, just the import of. In Ching China, there was a very high tax put on slave-owners, which freed most slaves, except in wealthy families. In Argentina, there was "law of the womb" - slaves' children were born free.

If the South had been fighting for abolition then they would have access to a couple million blacks to use as soldiers.