Trade is a gameplay mechanic in the Total War series. Trade generates income among factions, which is added to basic income through generated through taxation and other means.
Empire: Total WarEdit
Trade in Empire: Total War functions similarly to previous iterations with one major exception: the introduction of trading theatres and trade nodes. Accessing trade nodes in these theatres with merchant ships such as indiamen and dhows can generate substantial amounts of income depending on the quantity and quality of trading partners, to the point of making tens of thousands of gold per turn with a substantial enough trade fleet. On the downside, reaching these trade nodes may take dozens of turns, and they are under threat from Pirates and hostile factions.
The price of trade goods are impacted by supply. Having too many trading ships on nodes producing a type of good floods the market, driving down prices. Having too few ships, on the other hand, may not generate enough goods to adequately supply high demand. While more ships on a node produces more resources, they always produce fewer resources per ship. A balance can be fairly easily figured out by adding or subtracting ships from trade nodes one by one until income is maximized. As a general rule, each node can support around five ships. Trade goods can also be produced by plantations. Certain goods are produced in only specific regions. Tea, for example, is available only in India. Ivory cannot be obtained from plantations and are only available from trade nodes, allowing powerful seafaring factions to easily create a monopoly.
Napoleon: Total WarEdit
Trade remains largely unchanged in Napoleon: Total War. There are no trade theatres, and instead trade nodes dot the borders of the world map. Exploiting them is easier as they are much closer to factions' regions than trade theatres were in Empire: Total War. There are no pirates, either, so the danger of potential raiders is smaller.
Trade repesents the most lucrative short term method of making money. Whereas most buildings only pay for themselves dozens of turns after they are built, trade ships can pay for themselves in just one turn after reaching trade nodes in most cases. However, trade is riskier than investing in buildings, as trade fleets may easily be destroyed or chased away from trade nodes. Taxation is more profitable in the long term, as town wealth growth means that regions become wealthier over time; trade profits, on the other hand, remain largely static assuming the same number and quality of trade partners.
In some circumstances, trade is so profitable that it is better to make protectorates and trade with them instead of outright annexing regions. This is particularly true for factions that have a good trading fleet holding many trading nodes, and for protectorates holding richer regions: the richer a faction is, the more profit they generate through trade. Factions with only a few trading partners can expect large profits from each trading partner if they have lots of goods to export. However, as the number of trade partners grow, the amount of money made from each individual faction decreases (though the overall amount usually still increases). Therefore, a faction with many trade partners does not need to fear being cut off from any one trading partner as much because the loss of trade income isn't as large.
As in previous Total War games, trade routes of hostile nations may be raided for money. The amount of money gained depends on the number of ships raiding the route and the value of the trade using the route; moving the cursor over the route indicates how much of each. The amount gained usually isn't large, but it's the most useful way to occupy otherwise idle ships, and can help offset their upkeep costs somewhat.
Instead of providing various goods, trading nodes in the Peninsular Campaign simply provide "supplies". Supplies generate income by themselves, and generate additional income through trade. Trading is an integral part of the economies of Great Britain, Portugal, and Spain, since they initially don't control many regions and the world map doesn't have many resources, making trade easily much more profitable. It is unavailable to France, which is hostile to all other factions, though they still benefit from putting trade ships on nodes to gather supplies.
Total War: Shogun IIEdit
Trade routes are these lines one can see a little here and there. These routes are used for trading materials between provinces and giving both profit and materials needed for both provinces. Trading routes can be found both on land and over seas.
Longer trade routes can also involve more than two countries.
When a conflict calls, a third party country can raid other trade routes for profit. This is an act of war, instantly making the countries involved in the route hostile to the raider's clan.