"For a little while," Kagome said. "Then they get prosperous. There's no monsters to attack the fields, so the people who were on guard duty can shift to growing food. With good medical care people aren't sick as much, so there's more labor to spend on food production. The town starts to generate a surplus, so they can trade with other towns, transform excess food into other forms of wealth like better tools. The new tools make their labor more efficient, so it takes fewer people to do the same amount of work. That frees up more labor for other things...maybe they build a windmill, buy a loom, start planting non-survival crops like medical plants. Caravans start stopping there more often, since the town has wealth to buy with and goods to sell. Other people hear about this great new town and they move there."