International trade route (Civ5)

International Trade Routes are a new feature introduced in the Brave New World expansion pack for Civilization V. While the pre-existing concept continues to exist under the name City Connections, the new system allows you to establish long-term trading connections with other civilizations or City-States. These trade routes are supported primarily by the state, and not only by independent merchants; as such, they are established and controlled by you. They are almost essential for the income of your empire.
== Establishing International Trade Routes ==
=== Requirements ===
To establish International Trade Routes, you first need to develop your technology. Throughout the ages, various technologies expand your trading capacity, represented by the number of trade slots your empire has. The sum of all your land and sea routes can never exceed this total number. You can always choose to establish a different number of each kind (e.g., 3 land and 2 sea, or 1 land and 4 sea), up to your total maximum slots and according to your current needs.
At all times you may see at a glance the total number of routes and the number you're currently using from the top interface bar.
The following technologies each add 1 to the number of trade slots available:
* Ancient Era: Animal Husbandry, Sailing
* Classical Era: Engineering
* Medieval Era: Compass
* Renaissance Era: Banking
* Industrial Era: Biology
* Modern Era: Railroad
* Atomic Era: Penicillin
You can also try building the Colossus and Petra, each of which provides an extra trade slot and a free trade unit upon completion. When playing as the Venetians, you will have twice the normal number of trade slots available.
After you've acquired the scientific means for establishing Trade Routes, you need to produce civilian trade units - Caravans or Cargo Ships - which will conduct the actual trade. Think of them as governmental vehicles on which private traders may hitch a ride to the chosen city, where they are free to conduct trade for a fee. Trade units are produced (or bought with ) in the normal way, with the exception that when you reach the maximum number of your trade slots, you can't build any more trade units.
Each trade route you establish needs an appropriate trade unit (a Caravan for land, a Cargo Ship for sea) in order to function, and occupies 1 trade slot. Trade units are similar to aircraft and missiles in that they are based in cities, and can't be moved freely around the map. However, there's no maximum range for rebasing - a trade unit may be moved from one city to another on the opposite side of the map in a single turn. Caravans may be based in any city, while Cargo Ships may be based only in coastal cities.
Finally, be mindful of what Trade Routes you will need more, and don't produce unnecessary trade units. If, for example, you have 2 trade slots available, think of whether you'll need more land or sea trade routes instead of just rushing to produce the first trade unit available. The reason for this is that, once produced, a trade unit will occupy a trade slot, so you may find you're unable to establish the sea trade route you planned if you produced a Caravan to fill your last trade slot.
=== Route Mechanics ===
Once you have an appropriate trade unit in the city you want it, you can proceed to establish Trade Routes between cities. Note that Trade Routes can be established only along the native terrain of the unit, and with cities in range of the current unit's base. This range is given in number of tiles and is increased by a number of factors, such as the presence of a Road, the presence of certain buildings in the base city, and technologies. The specific trajectory of the route is calculated automatically so that it takes the shortest way available without passing through dangerous territory, such as a Barbarian encampment or near the cities of a civilization with which you're at war. Note that trade routes do not need an Open Borders treaty to pass through another civ's territory, and they can use other cities as shortcuts when hindered by terrain. For example, if you have a narrow (not larger than 1 tile) strip of land separating two bodies of water, and there is a friendly city on that strip that borders both bodies, your water trade routes may pass through that city.
When you decide to establish a route, first move an appropriate unit in a city in range of your destination. When you click on the Establish Trade Route option of the unit, the possible target cities will appear listed. If the city you want to trade with isn't there, then you may need to re-base your unit, or it means the city may not be in range yet. In this case, try to extend the range of your Trade Route via the means mentioned above. You can use the Trade Overview screen to see all potentially available trade routes, along with their projected effects, and plan your actions accordingly.
After you successfully establish a Trade Route, the trade unit starts circulating between the two cities (its base and the destination city), and will do so for some determined amount of turns. The circulation of the trade unit itself has no effect on the actual trading unless it's attacked by enemies (see below). The route effects are constant otherwise - you and your partner share benefits each turn, until the end of the trade. You can see how many turns are left for the current route from the Trade Overview.
Note that a trade unit is inaccessible while conducting trade - you can't do anything with it, select it, or control it in any way. After the turns left for the current trade route run out, you have to reassign it.
=== Land Routes ===
Land trade routes are established with Caravans over land. They have a default range of 10 tiles, regardless of terrain features along the route. Range is extended if the base city has a Caravansary, and if there are any Roads along the way. The Combustion technology also extends land range. Note that target cities have to be on the same landmass - you can't trade over a sea, even if it's a narrow sea.
=== Sea Routes ===
Sea trade routes are established with Cargo Ships. Their range is twice as much as that of land routes (20 tiles), meaning they can reach cities that are farther away. However, they can only be created between coastal cities. A Harbor in the base city extends the range of the routes, as does researching the Compass and Refrigeration technologies. Potentially, after developing all these upgrades, you can even conduct trade between continents.
=== Possible Destinations for Trade ===
You can establish trade routes with other civilizations' cities, with City-States, and even with your own cities. Of course, you have to be at peace with the destination city's owner in order to initiate trade, and you don't need to conduct any diplomatic talks to establish trade routes - think of it as if you were providing state-supported vehicles and destinations for your eager merchants to conduct their business at your direction.
== Principles of Trading ==
There are many benefits of International Trade Routes, and the trading mechanics are nothing short of amazingly versatile and interesting. When visiting foreign lands your merchants bring not only their goods, but also their knowledge, their culture, and their religion. And at the same time, they get exposed to these of the place they visit.
The main point of trading with other entities is to gain , while the point in trading with your own cities is to aid growing or struggling cities with and .
=== Trading with Other Civilizations ===
This is the most profitable kind of trading, but also the least secure. Before you even try, you need to keep in mind that both you and your trading partner will benefit from the trade, so it may not be a very good idea to trade with your main rival for victory, although the civilization initiating the trade always gains more benefits.
The act of trading involves not only monetary gain, but also exchange of a number of influences between both parties - culture, science, even religion. Here is what you both gain exactly:
* - The exact amount of a trade route owner and their partner gain each is determined by a number of factors, among which are:
** A base amount of 1 
** The total output of the origin city and the destination city: 5% of the output of each city, excluding revenue from other trade routes
** The diversity of resources available in both cities: +0.5 from each improved strategic or luxury resource
** Whether the city borders a River: Land trade routes to a city along a River receive a 25% revenue bonus
** Whether it is a land or a sea trade route: Sea trade routes provide double the revenue compared to land trade routes
** Other bonuses from certain buildings, wonders, social policies, or unique abilities of certain civilizations
* - Both partners gain some points each turn if they have each discovered technologies the other doesn't know. The benefit is the greater the more technologies the partner has that you have yet to discover. As of the Fall 2013 patch, cultural influence of the civilization establishing the trade route now also conveys additional points, provided they are at least at the Familiar level of influence to whoever they're trading with. More points are granted for higher influence levels.
* Religion - Both cities will exert their normal amount of religious pressure on each other. It is important to note that the usual religious pressure range restriction does not apply to trade routes. This means that Trade Routes can be used to spread religion to cities that could otherwise only be reached by Missionaries or Great Prophets. However, if a city is already exerting religious pressure on another via the normal religious pressure range, then a trade route between those cities will not exert any additional pressure.
* - Cultural influence benefits greatly from trade. The civilizations you establish Trade Routes with are more exposed to your than normal, thanks to your merchants' stories of the wonders of your empire. This translates to a 25% output bonus to this civ. When you're going for a cultural victory, target civs you need to influence more with your Trade Routes, using them as a backdoor for your .
Other civilizations may also establish Trade Routes to your cities. When you see Caravans and Cargo Ships coming regularly to your cities, you will know this is the case.
=== Trading with City-States ===
You can also establish routes with City-States. Those are less beneficial than trading with other civilizations, conducting nothing other than trade and religious pressure. Still, this might prove very important in some cases, and often in the beginning of the game the range of your Caravans and Cargo Ships simply isn't sufficient to reach another civilization, especially on the larger maps.
Obviously, City-States can't initiate trade routes, so establishing Trade Routes with City-States will greatly help you in gaining with them.
=== Trading with Your Own Cities ===
Apart from trading with other civilizations and City-States, you can establish trade routes to your own cities to aid their growth or increase their .
Establishing Trade Routes between your own cities generates either or in the destination city. The origin city does not actually lose the or being "transferred": its output is unaffected by the trade route. Note that in order to generate in the destination city this way, a Granary must exist in the origin city, while for you need a Workshop. Cities with neither of these two buildings cannot serve as bases for domestic trade routes, but can be their destination and beneficiary.
This can be a very good option to jump-start a city (or speed up the construction of wonders) in the middle and late game, when you have many other trade routes assuring your income.
== Plundering Trade Routes ==
Hostile entities may attack your trade routes. They can use the option Plunder Trade Route when they enter any tile that is part of the route.[dubious] However, only entities you're at war with may plunder your trade routes. Since you're always "at war" with the Barbarians, they pose an ever-present threat to your trades. Note that Barbarians may only plunder a Trade Route if they manage to intercept the trade unit itself, while hostile civilizations may plunder a route by positioning a unit anywhere along its path.[dubious] Plundering does not cost .
Plundering a trade route immediately ends the route and destroys the unit that was servicing it. The plunderer gets a nice amount of , but also receives diplomatic outrage from the other (third) party which was participating in the trade. Plundering a trade route also constitutes an act of war against the owner of the route.
A trade route is automatically plundered when its trade unit moves onto a tile containing an enemy unit capable of plundering.CvTradeClasses.cpp - CvGameTrade::StepUnit() Units cannot plunder trade routes while embarked.CvUnit.cpp - CvUnit::canPlunderTradeRoute() It is sometimes[clarify] necessary to move a military unit above a trade unit (as opposed to merely the trade route) in order to plunder.
Plundering may become an effective tactic while at war, carrying a nice profit for you. Otherwise, you also have to be aware of the consequences, so consider it carefully. When "backstabbing" a trade partner, position your units in such a way as to be able to plunder the trade routes they've opened with others in a short time. You should also try to cancel any trade routes you've opened with them, because after the start of the hostilities they'll surely return the gesture.
== References ==
Category:Game concepts (Civ5)
Category:Civilization V: Brave New World