I see your point about pioneer America as a model for Bakunin, but as far as I know he didn't support the Southern states, maybe am I wrong 'cause he changed idea after 1861, see the link at: https://libcom.org/files/BAKUNIN AND THE UNITED STATES.pdf, page 325-326 (sorry if I repeat myself).From what I have to hand I can see that Bakunin was impressed by pioneer America which in his eyes was socially free, utilising vast fertile open spaces for productive activity with little or no government in the European sense. He appeared to have nothing to say about the natives who were being displaced but that was normal for the European perspective at the time.
He condemned capitalism in America as it demanded high tariffs because it was unable to compete with European manufacturing. In other words protectionism propped up the state. This is where he came to support the Southern states as they had no manufacturing base so paid the higher tariffs. However he did argue that the social question that industrialisation was causing in Europe was increasingly applying to the United States.