I wonder what an inefficient way would look like.
But it's counterfactual. It took severe violence plus 100 years to get there. Plus another 60 (yikes) to get to where we are today.
That's horrible! But nothing about that reality suggests to me that there was a less-violent or speedier way to get there. Governments are made of people.
Getting there was a worthwhile goal. I don't think there's a "but at what cost?" debate here.
So it sure doesn't feel "efficient", but it might be the "most efficient possible" in the human world.
Sometimes, progress is measured by funerals.
It is not like north would march in there to stop the slavery. There was an anti slavery army - John Brown with his, like, 20 or so people attacking south.
African Americans as second class citizens were in fact much better off then them being slaves.
So, we can say that it was violence problem that got solved by violence. Not just political problem.
Moreover, that sentiment was literally expressed by slavery opposition back then. Afaik, the sophistry about "any government is violence therefore, it is the same, que" was not all that much thing back then.