http://leftychan.i2p/ga/res/8422.html
Think about it, it could be made really naturally too, you would need to add a system so that you could fight a villager to subjugate him, and make him grow crops, and if he happens to be from your village you can only make him give you a quota of grain, but if he is from another village, then you are allowed to make him give you everything. so that the first one will be more profitable at the beggining, but as you get better tools, then they become more equalised, and you are incentivised...