What training techniques get people to see certain other people as less than human?

In Nazi Germany, a whole culture saw Jews as less than human. In Vietnam, the army was trained to see the Vietnamese as Gooks, so they could kill them. In Abu Ghraib and Guantanamo, certain units within the army and CIA became able to torture other humans. They could even take pictures of it, and laugh about it, even though they were doing things to people they wouldn’t do to a pig.

I believe you have to dehumanize people in order to be able to torture them, or to be able to believe it is ok to kill them. Either that, or you have to be a sociopath. However, I think we may all have sociopathic tendencies within us, and certain training techniques can help us to close down our senses of morality, and let the sociopath loose.

What are those techniques? How can we turn moral and ethical people into sociopaths?