Cheap energy made machinery possible which made slavery obsolete. Slaves went the way of mules and oxen; all three of which should make a comeback. New bankruptcy laws anyone?

Thats dumb. Energy costs would have to rise 100 fold for people to even start considering slavery as a possible replacement for heavy machinery. 100 slaves cant compete with 1 heavy backhoe and they take more energy to feed anyways than the backhoe.

Thats before the extra cost of keeping them locked up. Energy costs can't rise that high simply because the replacements are too easily within reach for far too long of a timespan. Nuclear and wind complimented by hydro are cheaper at electric production than oil today and are close to competitive with coal, and for all practical purposes unlimited. Slavery became obsolete when energy was far more expensive (kw/hr per man hour) than it was today with far inferior technology to make use of it. The notion of a return of slavery for industry is ludicrously naive.