I know this is an old thread but I couldn't find any good guides to trade. Anyway, here's my version of events.
Trade: the water religion.
Civs
There is only one Civ in Warlords that gets any extra benefit from trade. And that is the Carthaginians. The Cothon (harbour) gives an extra trade route. And that is awesome.
When to use.
When there is lots of coast and you aren't isolated. You are going to need coast to make anything of trade. One coastal town with decent production (for making wonders and the harbour) required to make it worth while. The more the better.
What to do.
So you have lots of coast. Open borders with your friends (writing) You are going to make a rush for two wonders. The first is the great lighthouse. The second is the temple of Artemis. Try to get both in the same city. A city is going to have 1 trade routes by default. And they will be worth 1 gold if they are local, and 2 or maybe 3 gold if they are with other civs. (roughly - depends on size of foreign city).
So 1 or 2 gold per city if you link with another civ and open borders. Nice.
Now the GL is going to add 2 more trade routes to the coastal towns. The temple of Artemis is going to double the value of those trade routes. A harbour is then going to multiply that by another 50% (+ make people more healthy) and a Cothon would give you another trade route.
In the Artemis city build walls and a castle for another trade route. Its worth it.
So now you have 1 routes by default. 1 more from learning currency (which you prioritise). 2 more from the GL. 1 more from the castle and possibly and extra one from being the Carthaginians. 6 routes in that one city. 5 in other coastal cities.
And they get 2 or 3 gold each * 100% from Artemis * 50% from your harbour/Cothon.
So 6 routes at roughly 8 or 9 gold each in that one city. That's a base gold rate of more than 50 in that one city! Do the religions earn you anything like that early doors? Not even close. And that base 50 something can be combined with libraries etc to boost it further. Its a massive tech boost.
Also note that both the T of A and the GL produce Great Merchants quickly that you can add for even more gold.
What to avoid?
Mercantilism. Avoid it like the plague. It will smash your gold earning as foreign trade routes become banned.
Economics and the Corporation.
Technically both give you an extra trade route. Sounds awesome. But the Corporation is going to obsolete your GL. You lose two routes on coastal cities in exchange for one. Assuming most cities are on the coast (hence the reason you chased trade) then delay this tech. Economics also gives you an extra trade route, it does kill your castles off though. A straight swap in those cities. I wouldn't rush for them as trade will die. See below
What happened to my trade?
At some point all the gold stops rolling in. It took me a while to work out why it suddenly stops. And the answer is BANKING. Not you discovering banking. Your trade buddies. They then switch to Mercantilism and you get left on your own with local only trade routes as they can't trade. The lights go out and your gold stops there and then. This is the death of trade.
You can try to give them education and economics cheaply in the hope they change to the free market, but I have had varying degrees of success with this. Other civs are mostly not interested. One free specialist per town isn't worth the 20 odd gold per town you now lost and 50 in your Artemis town, so its time to move on.
So my advice would be, use the massive gold boost you get early and at construction/currency use that gold to fund an infeasibly large army of catapults and hopefully elephants. Then go find someone - and crush them assuming you don't rely on them for the trade. Otherwise dash for Military tradition and gunpowder. You'll hopefully get these just as the trade begins to die. Whilst other civs are messing about learning economy and the corporation (which are not much use until everyone stops using merchantilism anyway) start a war. No one can come close to the gold you are making or the speed you are teching, religion or not, so press home this early advantage. Its only going to last until your opponents get banking. You have decent window. From about the time you have currency to all your opponents discovering banking. (If you are tech trading I should think it obvious not to give banking to people.)
If anyone else has any opinion on trade, please add. Trade seems to be largely ignored but it can be very useful.
