Use the following trick to totally slaughter the enemy villagers but not keep them. First, get the Siren and Volcano or Earthquake wonders. Charge them up so you can cast both of them at about the same time. Ccast the Siren wonder in a heavily populated area. As soon as every one comes, cast the Earthquake, Volcano, or Hurricane where all the people are gathered or next to the Siren herself. They will not be able to build soldiers, and will all be dead quickly.