Trade is based on the notion that you swap what you do not need or do not want, for something you do need or want. For example, you want a new car and you have more money than you need, so you buy a car from a dealership which has cars but needs money. Or perhaps you are better at playing a certain sport than anyone else on Earth, so you swap your time for vast quantities of money at one of the top clubs (and then, oh, the cars you will buy!)
All of this is based on the idea of people needing and wanting different things, and having different things.
In Illyriad today, all settlements can make everything if they choose to do so, so there is nothing that you cannot make for yourself. On the other hand there is nothing that you have that is useless to you. Everything you want, you can get through manufacturing, with little need to trade. As a result, trade in Illyriad today is fairly limited.
But all of that is about to change.
Imagine if you awoke one morning to find that you had, near your towns, a mine and a patch of woodland where you can gather rare gems that are useful in magic. Now you don't need to cast that many spells that often, so you can easily have more gems than you need. You could stockpile these, but you could also sell them. Now, you may want to defend your new-found resources, and you may want your spearmen to be able to defend well on both mountain (mines) and forest (woods) terrains; so, you may decide that to help your troops do this better you would like to equip them with defensive spears whose manufacture requires a rare metal from the far north.
Now suddenly, it is worth you getting involved in trade. You have something that magic-using cities want, and you would quite like some of that northern metal. And in order to buy these unusual items you will now have access to a specialist market - found at your nearest Faction Hub.
The result is that you have lots of choices to make. Do you use two building plots in order to gather the herbs and minerals? Do you sacrifice a plot to make those superior spears, or would you rather just pay extra for the finished spears and let someone else do the manufacturing?
And for the actual trading, do you rely on players who have specialised as middle-men, simply Accepting the sell orders that they have placed in your local Faction Hub, or do you maintain your own specialist trade units in order to access distant Hubs and place your own trade orders?
When all of these extra resources are in, you will still be able to produce everything that you absolutely need. Iron, wood, food, etc, everything a town requires, will still be produced in your towns. But now, you may find yourself with a shopping list of other things that you want, and you may also find yourself with the ability to gather or manufacture things that you don't need but other people want.
Different players will react to this differently. You could, if you wish, fill your town with specialist crafting buildings to make troop equipment. You could completely fill your town with gathering buildings (though you'll want to keep a slot for a market to ship the goods out, and very few people will have access to large enough quantities of resources to get a benefit from that many gathering buildings). And you might consider giving two or more plots over to trade buildings.
Or, of course, you might decide that some or all of your towns have other functions, perhaps preferring to dedicate all your town slots to the advanced magic or military buildings, leaving all the gathering and manufacturing and trading to others. Your choices will depend on the stage of your town's development, what new resources you happen to have near by, and what style of play you prefer (military, magic, gathering, manufacturing, trade).
The result of different players making different decisions will be that their town buildings will become highly varied, and that their settlements will be producing and consuming different goods. For players who want to trade that means plenty of new opportunities. And for everyone else that means lots of choice in how to build up your cities.
