slavery is still very much alive today. Slavery is the trade (for goods or money) of one human being to be owned by another. It is remembered in Great Britain, USA and the countries that slaves were traded from because of landmark decisions.
Slavery occurs but we call it different things - human traffiking is one term. I listen to a lot of American 'Gangsta' hip hop. Not because it's great, but because it's a statement about a place where a group of people trade. They trade insults, they trade drugs, they trade women. It is now less an issue of colour, as it very much was 200 years ago. 50 Cent and his G unit 'pimp' women. Those women are Black women. White Russian traffickers traffic white women. Chinese slave chinese... It hasn't ended, the dynamics have changed slightly. Interestingly, it's still often men who lead the slavery, and women who are majority victims of slavery.
Imprisonment is a different issue altogether. As a method to change a individual's behaviour there is evidence to show it doesn't work. The problem is that it balances the tension between public need to see criminals punished and the politicians need to be seen to tackle crime.