Were they a specific ethnic or religious group? When Pol Pot wanted to cleanse the society, what did this mean exactly? How was it an attempt to restore Cambodia to an agrarian society? I can't wrap my head around any of these ideas. It just seems like senseless violence. The Holocaust makes more sense to me, even though it is equally horrible, because the target seems clearer: remove undesirables from society.
So, in essence who were the undesirables of Cambodian society, and why did they need to be exterminated?
How was it an attempt to restore Cambodia to an agrarian society?
It wasn't, there were many successful and not-so-successful attempts to create industries. The victims came from all sectors of society, although officials from the previous regime were targeted more than most. Many of the victims were those who disagreed with the center, or were perceived as doing so.