|Available only with the Mare Nostrum DLC enabled.|
Trade leagues () are a type of defensive diplomatic relationship that can involve multiple countries. Merchant republics and Veche republics can form trade leagues and invite other countries to join them; this gives both the leader and the members various diplomatic and trade-related benefits.
Creating a trade league
Any merchant republic or Veche republic can create a trade league by inviting other countries to it. Only countries with a single province can be invited to be a member of a trade league. The merchant republic that created the trade league may have more than one province at the time of formation and may gain more afterwards, but if any of the other members gain additional provinces they will automatically leave the league. If the leader is annexed or changes to a different form of government, another merchant republic or Veche republic in the league takes over leadership. A new leader will also be selected if the current leader drops below −50prestige. If there is no eligible leader, the Trade League disbands. Members can leave a league at any time, excluding Trading Cities.
The factors that influence an AI nation's willingness to accept an invitation to join a Trade League are (not complete):
|Size of Trade League||−10 per existing members over 5|
|Attitude towards proposer|
|Friendly or Allied: +50|
|We have a royal marriage||+10|
|Proposer's diplomatic reputation||+5 per positive point|
|−5 per negative point|
|Target's opinion of Proposer||+1 per 4 positive opinion|
|−1 per 4 points of negative opinion|
|Nation has a religion not in the same religious group||−20|
|Nation has a different religion within the same religious group||−10|
|Proposer army strength power compared to target nation||+20 to −20|
|Proposer navy strength power compared to target nation||+10 to −20|
Trade leagues act as defensive alliance between all members, but consume only a single diplomatic relations slot. If the leader embargoes another country, all members automatically embargo that country too without a penalty. If any members in a league gets embargoed, the leader gets a special “Trade League Dispute” casus belli on the offending country.
- The trade league leader gets an automatic “Trade Dispute” casus belli on any countries they would be able to generate such a casus belli on via spy action.
- The trade league leader gets 50% trade power from all the league members.
- The trade league leader gets a +2.5% bonus to trade steering for each member in the league.
- All members get a +20 relations bonus with all other members.
- All members except the trade league leader get a +0.5% goods produced modifier for each percentage of trade power in the local trade node controlled by the trade league leader.
- All members get a +20% bonus to their ship trade power.
Merchant republics or Veche republics that have a Trade League are able to create a new one-province-minor out of one of their provinces (even during war!) from the province view, in the same way as a Client State. This new nation will become independent, but part of their Trade League. It will always inherit the creating nation's state religion. The player can decide upon Trading Cities' name, shield and color, similar to creating a custom nation; national ideas are randomized, however. The first Trading City created in the world has the tag T00, the second T01, and so forth.
A Trading City can create trade posts and boosts goods produced in the trade node just like a merchant republic, but cannot lead a Trade League and thus not create other trading cities. A Trading City that gains an additional province will immediately become a Merchant Republic; make sure this is not possible for AI trading cities in your trade league to achieve, since they will attempt to expand in spite of their government form. Note that if the Trade League is somehow disbanded, or if a player-controlled Trading City leaves it, it will retain its government form until a second province is acquired.
There can only be one Trading City in each Trade Node for a Trade League. Unlike typical trade league members, a Trading City cannot be kicked out or be diplomatically vassalized by a non-member. In fact, you are stuck with it unless you convert to a Monarchy or Theocracy, or give away its province or transfer its trade power to someone else when you lose a war (or, counterintuitively, when you have reached 100% war score, which forces all demands or offers to be accepted). As a probably unintended exception, Trading Cities may still leave by becoming a tributary, since they are not coded as subjects. Hence, do not make a Trade City from a province that neighbors a Steppe Horde or a country with an Eastern religion, or make the potential tributary overlord your subject first.
The government type gives the following modifiers, which are similar to those of a standard Merchant Republic:
- +33% Caravan power
- +10% Trade efficiency
- -20 Maximum Absolutism
- +1 Number of states
- Fixed Duchy rank
- has the same factions and election cycle as a Merchant Republic