To get this achievment, just slay all 100 villagers of Everlight or Nordberg.
If you play the game as a Destructor, you will automatically have this achievment because to be a Destructor, you have to slay everyone.
Each time you slay a villager, a counter is displayed giving you the number of inhabitants remaining. Don't forget villagers hiding themselves in house... Destroy each house and they will appear and stay not far from ruins of their own home.
It is not my video but it will certainly help those who wants to get "Town Razer" achievment. (it shows the achievment after killing the last villager in Nordberg)