I think the primary difference is profit motive. In the USA there is a HUGE incentive to have an endless supply of prisoners not only to fuel private prison corporations, the logistical suppliers, law enforcement, and most importantly, USA's answer to China's sweat shops, prison labor. In prison, prisoners work for pennies producing goods sold on the open market. There is such a massive prison industrial complex in the USA, over 1% of our entire population is incarcerated. Slavery never really ended here, it just changed form.