Peasants can be acquired in two ways: Firstly, the peasant population will slowly increase each day based on Peasant happiness (you can gain up to 4 peasants a day this way). Secondly, if you capture houses in quests (or some PvP battles), you can gain peasants. A good example of this would be the Lumber Raid or Kill the Beast quests (you will gain 1 peasant for every few houses you capture)
