In the world you will find settlements with a wooden wall around them. They're always called ''s hamlet' or ''s village'. These settlements are not owned by human players, so you can't make contact with the owners.
My Kingdom refers to them as Barbarians. If you buy a Dragoman unit you will be able to trade with them when visiting their settlement. At their settlements they often have uncommon goods at good rates! Some Barbarians also offer their locally produced goods through the market.
Make sure you keep Barbarians as your friends, especially in the beginning. Angry Barbarians will not sell their goods to you, while being the only seller of specific commodities in an uncrowded area. If you manage to make a Barbarian your friend (pay respect at least more than 5 times) they might pay you respect every once in a while by giving you uncommon commodities.