Diplomacy in EU4 is the system that involves all relations and actions with other nations. Relations can be increased through alliances, coalitions, common wars, common rivalries, decisions, events and having a diplomat improve relations. Relations are decreased by declaring war, being rivals, sending insults, having a different religion, breaking/dishonoring an alliance, events and decisions. Diplomacy is a bilateral system and will affect relations on both sides of an agreement.
Reasons for a nation's opinion of another are displayed in tooltips wherever opinion is shown. The total is capped at +200/-200.
Diplomacy is conducted by diplomats, and the diplomatic options available to diplomats depends on a country's technology and ideas. Diplomatic options are split in seven categories: alliance, influence, relations, dynastic, covert, economy and access. The emperor of the Holy Roman Empire has an extra category: Emperor actions. The Papal controller also has an extra category: Papal actions. The declare war and sue for peace diplomatic options are found outside of these categories.
- 1 Diplomats
- 2 Diplomatic relations cap
- 3 Diplomatic reputation
- 4 Diplomatic actions
- 4.1 War
- 4.2 Alliance actions
- 4.3 Influence actions
- 4.4 Relations actions
- 4.5 Dynastic actions
- 4.6 Covert actions
- 4.7 Economy actions
- 4.8 Access actions
- 4.9 Papal actions
- 4.10 Emperor actions
- 4.11 Great Power actions
- 5 Other
- 6 Achievements
- 7 Footnotes
A diplomat is required to perform most diplomatic actions. Some actions - improving relations, annexing a vassal, building up a spy network and counterespionage - will occupy a diplomat indeifinitely or until completion of the task, unless the diplomat is manually recalled. Actions that will occupy a diplomat for a period of time will display a diplomat icon () on their button. Other actions are immediate.
When initiating a mission, a diplomat takes one day to reach the target country and begin its mission. After completing a mission, a diplomat will be unavailable while he travels back home, the time which scales based on the distance between one's capital and that of the target country. The precise travel speed of diplomats is 20 distance per day.
Diplomatic relations cap
The number of other countries a nation can have diplomatic agreements with is limited. Each relation over the cap costs 1 diplomatic monarch point per month. The limit only counts for the number of different countries with whom an agreement has been closed, not the number of agreements. Having multiple agreements with a single nation only counts as one diplomatic relation.
Agreements that count towards the cap include:
- Royal marriages
- Having a vassal or junior personal union partner
- Receiving military access
- Supporting independence
- Having a client state
Agreements that do not count toward the cap include:
- Granting military access
- Receiving or granting fleet basing rights
- Receiving or granting loans (disabled since patch 1.4)
- Warning other nations
- Giving subsidies
- Having a colonial subject or protectorate
- War reparations
- Transferring trade power (including enforced 'transfer trade' as part of a peace agreement)
- Having vassals who are members of the empire as the Holy Roman Emperor, if Revoke the Privilegia has been passed.
- Receiving conditional military access (e.g. within the HRE due to being in a war with the Emperor, or with someone else who has access)
Increasing the diplomatic relations cap
The base diplomatic relations cap is 4 diplomatic relations. It is affected by the following:
|-2||Tribal government Duchy|
Ideas and policies:
Certain events may also give a temporary increase in the relations cap.
Diplomatic reputation positively affects both subject relations and relations with sovereign nations.
With subject nations, each point of diplomatic reputation gives:
- +5% chance to inherit lesser partner in a personal union
- +1 diplomatic power used per month while annexing vassals or union partners
- -3% to the liberty desire of all subject nations
With other countries, each point of diplomatic reputation gives the following bonuses when accepting diplomatic proposals:
|Offensive Call to Arms||5|
|Establish and Request Protectorate||3|
|Transfer Trade Power||3|
|Ask for Military Access||3|
|Ask for fleet basing rights||3|
|Request to share maps||5|
|Demand unlawful territory||3|
|Grant free city status||3|
Gaining diplomatic reputation
Diplomatic reputation can be increased by the following modifiers and ideas:
- Legitimacy: -1 at 0 legitimacy to +1 at 100 legitimacy
- Overextension: -2 per 100%
- Trading in Ivory: +2
- Statesman advisor: +1
- Subjugation of the Papacy (Triggered Modifer for Catholic Nations): -2
- The Occupation of Rome: -1
- Annexed Vassals: -3 for 10 years
- Being a member state of the HRE: +1 for non emperor HRE members
- Institute Reichsregiment (HRE reform): +1 for the Emperor
- Enact Gemeiner Pfennig (HRE reform): +1 for non emperor HRE member
- Hindu state with Ganesha as patron deity: +1
- Buddhist state with balanced karma: +1
- Catholic state with Papal Influence spent on the "Send papal legate" option: +1 for 20 years
- Reformed state with stability focus: +1
- Tengri state with Catholic syncretic faith: +1
- Fetishist state: +1
National ideas and traditions, idea groups and policies
Declaring war initiates a military conquest against the target country. A casus belli can be selected and the allies of both sides are shown in the declare war screen. Winning battles, achieving the wargoal, and occupying provinces accumulates war score for both parties, by which peace terms may be agreed upon. At war a country can offer a peace deal (sue for peace) or an unconditional surrender.
以下内容需要完善：subsections 'Invite to trade league' and 'Kick from trade league'。
Form coalition against
A coalition is an alliance of nations who have bonded together against a common enemy because of this enemies' very high aggressive expansion. Coalitions members will automatically be offensively and defensively called to arms in any direct war between a coalition member and the coalition target.
Nations may support the independence of a nation if the target nation is a subject nation and has a liberty desire of over 50%. If the target nation declares a war of independence, all nations supporting its independence will automatically ally the target nation and join the war against the former overlord of the now (temporarily) independent nation.
A nation may rent out their armies to another nation in exchange for payment, while maintaining manual control of the army. A maximum of 20 regiments can be rented out simultaneously.
The enforce peace action demands that the leading attacker in a war make a white peace with the leading defender. Refusal will bring the enforcing nation into the war on the side of the defender. The following conditions must be met in order to enforce peace:
- The enforcer must not have a truce with the leading attacker.
- The enforcer must have at least +100 relations with the leading defender.
- The attacker must have -25% warscore or better.
Enforce peace is a useful method for entering wars without triggering any automatic defensive call to arms from the opponent. For example, European powers outside the Holy Roman Empire can use enforce peace on empire members to enter wars against them without having to fight the Emperor. Enforce peace can also turn the tides against a rival's offensive war.
Additionally, enforce peace may be used by an overlord to take command of a protectorate's offensive war, in which case the overlord becomes the leading attacker.
Vassalization makes the target nation a subject nation of the country that offered it. Vassals are automatically called to their overlord's wars and pay a portion of their tax income.
Breaking vassalization cancels a subject nation's vassalage and makes them independent. This action costs -25 prestige and -200 relations penalty with the former vassal, and results in a truce of 5 years with the former overlord. Vassalization cannot be canceled when a truce exists with the target.
Revoking a march changes it to normal vassal status, allowing for it to be annexed. This action costs -1 stability and results in a -200 relations penalty with the subject.
Diplomatic annexation incorporates a client state or vassal into the overlord's domain, resulting in direct control of the former subject's territory and military. This action occupies a diplomat for its duration and costs diplomatic power.
Diplomatic integration incorporates a junior parter of a personal union into the senior partner's realm. Like diplomatic annexation of vassals and client states, completion results in control of the junior partner's territory and military, but also gains control of the junior partner's vassals, colonial nations, and protectorates.
Sending a warning to a target country results in a defensive call to arms if the target attacks one of the warner's neighbors. Rejecting this call to arms only incurs a penalty to trust with relevant nations. The list of neighbors for any nation can be found in its diplomacy tab by filtering its relation list to neighbors only. A country cannot warn another country it is already warned by, or that is not significantly weaker. A warning lasts for 20 years and can be issued again once it expires.
Threaten war is a diplomatic action which lets a nation demand a province that it has a claim or core on. If the demand is accepted, the province is transferred to the demanding nation. If the demand is not accepted a war with the Conquest casus belli for said province. War cannot be threatened over a country's capital (it cannot be targeted at an OPM) or if a truce exists with the target country, and nor can a subject nation threaten war. Successfully demanding a province will cause the threatening country to gain aggressive expansion as if the province had be conquered in a peace deal and the target nation to lose -10 prestige. This also creates a 5-year truce between the two nations. A country will relinquish a province if the relative strength of the demanding country's alliance outweighs the relative worth of the province and the alliances of the threatened nation. The AI is more willing to give up provinces that the demanding country has a core on, and much less willing to give up provinces if that country has recently demanded another province.
Factors that influence the AI's willingness to giving up a province are:
|Province is not a core of the threatening nation:||-20|
|Relative strength of alliances:||-100 to +100|
|Relative worth of province to target's entire development:||-1 to -200|
|Recently gave in to threat:||Base of -120, increasing by +1 per month after truce ended|
When sending a diplomat to improve relations for the first time or when the improved relations value has decayed to 0 doubly improved opinion is gained on the first tick. The rest of the relations improvements take place at the end of each month.
Send an insult
Sending give the target country the Diplomatic insult casus belli on the insulter for 1 year and lower relations by -50, decaying by +5 per year. Insults are useful for negating the -1 stability hit of declaring war on nations that have +100 relations of the aggressor. Insulting a rival also grants +5 power projection, decaying by -1 per year, provided that the insulter neither has a truce with them nor already has power projection from a previous insult.
- For the dynastic effects of royal marriage, see Ruler#Royal marriage
- For information on personal unions, see personal union
Countries ruled by monarchs may arrange royal marriages with others. This improves relations by +25 while in effect. Attacking a country with whom a nation has a royal marriage results in -1 stability and +1 war exhaustion. Note that this penalty will not occur except through a standard declaration of war; to circumvent it, the player may find it useful to Threaten War over a province that the target will refuse to cede.
Upon the death of a Christian monarch with no heir, a ruler from the dynasty of a more prestigious country that shares a royal marriage may rise to the throne. If the countries already share a dynasty, a personal union may result instead. Personal union partners function militarily like vassals. They do not pay a portion of their tax income but may be inherited. Higher prestige increases chances of gaining the crown of a royal marriage partner for a country's dynasty, either independently or as a personal union.
Royal marriages are unavailable to theocracies and republics, with the exception of the Dutch Republic. Christians may only marry other Christians. All non-Christians may marry each other, but personal unions will only occur for Christian nations.
The factors that influence a nation's acceptance of a royal marriage proposal are:
†: Distance between borders can only be seen in debug mode.
Break royal ties
Breaking royal ties ends a royal marriage. This results in -1 stability and -1 prestige. Furthermore, the relation with the target country is decreased by -75. The stability cost may be negated by completing Diplomatic ideas or being the Curia Controller. The death of the ruler who proposed the marriage will also end a royal marriage without penalty.
- For information on improving chances of obtaining a personal union, see Personal Union
Claiming a throne gives the "claim on throne" CB, a military means of forcing a personal union.
The requirements to claim a throne are as follows:
- Target has a royal marriage
- Target shares the same dynasty as claimant
- Target has a weak claim heir or no heir
- Claimant has more prestige than target
Claiming the throne of a country results in the following diplomatic effects:
- -50 relations with other royal marriage partners
- -100 relations with the target country, and incur a loss of -20 prestige.
- Claimant gains "Claim on Throne" casus belli against the target. The war score cost to enforce a personal union is 84% regardless of the target's size.
Note that while some allies may be willing to join a conquest war, they will not join a claim on throne war or succession war, due to opposition to a successful personal union. The gained casus belli lasts until the target country produces an heir with a strong claim or a new heir rises to the throne.
The claim throne diplomatic action is only possible for Christian nations as no other religious group allows personal unions. While the Dutch republic, oligarchic republic, and elective monarchy can have royal marriages, their thrones cannot be claimed as they do not have heirs.
Supporting an heir is an action that can be initiated on nations with an elective monarchy (which can only be gained by event for 波兰 and the 波兰立陶宛联邦, or by using a custom nation). Any nation that is in the same religious group as the country with elective monarchy can support an heir.
In an elective monarchy, each nation that has supported its heir in the current election cycle has a possible heir to the throne with an associated amount of support. A diplomat must be sent in order to support a nation's own heir in an elective monarchy,
The probability of increasing the heir's support every month by 1 is as follows:
Upon the death of the elective monarchy's ruler, the heir with the most support rises to the throne in the elective monarchy.
If a foreign heir arises, the country that provided the heir gains:
If a local noble rises to the throne, the elective monarchy loses -20 relations with all countries that supported an heir in the election.
Diplomats can be send to other nations to build up a spy network, or to practice counterespionage and increase the chance of catching spies sent by the target nation. When a spy network has grown enough, espionage actions can be undertaken, which do not require sending a diplomat. Most of the espionage actions require certain ideas from the espionage idea group in order to become available. Actions that do not need this group are fabricate claim, support rebels and justify trade conflict. Completing the espionage group will give access to various powerful actions. One example is the vetting idea, the first of the idea group, which grants a discount to technology cost depending on the difference in technology level between the home country of the spies and the target country, as well as the size of the spy network there. Covert actions are described in more detail on the Espionage page.
Transfer trade power
Ask a target non-subject nation to transfer a percentage of its trade power to the proposer. While a transfer of trade power is active, the two nations involved cannot declare war on each other, and will also receive a mutual relation bonus of +20 per 100% of power transferred. The agreement does not count towards each country's diplomatic relations limit.
The factors that influence an AI nation's desire to accept a request to transfer trade power are
Reduces the trade power of the target country in every trade node the embargoing country has trade power in, depending on several factors. Embargoing a rival grants power projection. Embargoing a non-rival gives a penalty to trade efficiency, but can give a net gain in trade power share (and hence income) if the other country is very dominant in an important node.
The following bonuses apply to embargo efficiency:
The final value is rounded down to the nearest integer. The relation bonus will last for 5 years. Additional gifts sent during this time will have no effect unless it would increase relations more than previous gifts did.
Allows a nation to loan out money to other countries for interest. When the loan is due to be repaid, the loan-taker can instead choose to keep the ducats. This will give the loan-giver a casus belli. This is disabled for any AI country, as it is basically a "free CB" button due to the AI's misuse of loans.
Transfer a specified amount of money each month to the target country for a certain duration. The sender may transfer between 0.1 ducats and +50% of its monthly income to the target country each month, adjustable in increments of 1% of its monthly income. The duration of the subsidy can be set between 10 and 400 years, adjustable in increments of 10 years.
Maintaining subsidies will improve the target country's relations with the subsidiser each month, up to a maximum of +15. The accumulated relation bonus is completely removed when the subsidy is cancelled or expires. Since there is otherwise no penalty for terminating a subsidy early, it is generally good practice to set a long subsidy duration unless diplomat time is severely constrained. The relation bonus is
All monthly income mentioned in this section refers to the monthly income as reported in the ledger. Be aware that the target country's total monthly income will therefore include this monthly subsidy once the ledger is updated after the establishment of the subsidy. This imposes significant diminishing returns on the relation benefits of a large subsidy, and encourages one to maintain smaller subsidies over a longer time frame instead.
Example: Country A has a monthly income of 10 ducats, and country B provides it with a monthly subsidy of 5 ducats. The reported yearly relations boost will start at +6 per year (B's subsidy is 1/2 of A's income), then immediately drop to +4 per year after the first month (the subsidy is now 1/3 their income).
Subsidies do not consume a diplomatic relations slot. This makes them a valuable tool for blandishing future targets of diplomatic vassalization or annexation.
A province can be sold to an another nation for a price of 0 to 2,000 ducats at a cost of -10 prestige. Both the buyer and seller must be at peace, and neither can be rivals of the other party. Only one province can change hands in a single transaction. The AI will only offer to sell isolated provinces, particularly if it is unable to core them. When the sell province button is clicked, the province to be sold can be chosen together with the price that will be asked for it.
Factors that influence an AI nation's willingness to buy a province:
|Province is priced above current treasury of buyer||-1000|
|Buyer has no core or claim on province that is of a different culture group||-1000|
|Buyer has no core or claim on province that is of a different religious group||-1000|
|Buyer has no core on province and is currently overextended by any amount||-1000|
|Buyer has no core on province that is part of the Holy Roman Empire||-1000|
|Price||-1 for every 1% above above 50% of buyer's treasury|
|Province is adjacent to buyer||+10|
|Province has the same culture as buyer||+10|
|Province has the same religion as buyer||+10|
|Price||-100 to +100 based on development of target province|
A province can always be bought as long as the price is affordable if:
- Buyer is a subject and seller has a core on the province
- Buyer has core on province
Additionally, it is not possible to sell a province to a colonial subject if the province is not in its colonial region. If the province is particularly undesirable to the buyer, then its base value and associated price modifier will both be halved.
Selling provinces to a vassal is one method of saving administrative power by letting the vassal core the province. It is useful for avoiding overextension in the short term, and exchanges immediate administrative coring costs for diplomatic annexation costs later. The DLC enables giving provinces to vassals directly via the subject interactions interface, making selling provinces to them unnecessary.
As AI nations place a very high priority on core creation, one can delay their research progress in administrative technologies by selling them provinces with a high coring cost. This can be particularly useful if the next administrative technology would otherwise unlock a troublesome idea group (e.g. AI Portugal's first idea group is always exploration).
Navies can be sold to other nations for a price of 0 to 1000 ducats. If the target nation accepts the proposal, the fleet in question will transfer its allegiance to the buyer. In order to be able to sell ships to a nation, both sides have to be at peace and cannot be rivals of each other. After pressing the button, the fleet that is to be sold can be chosen together with the asking price. When offered to buy a fleet, the AI will want to hold on to a certain ratio of ships (for example, most countries on the Atlantic coast don't want to buy galleys) and will never go above their naval force limit. In order to be able to sell ships, the buyer has to have a fleet within supply range of the target nation. Fleets outside of the receiving country's supply range are not available to sell.
The factors that influence an AI nation's willingness to buy ships:
This allows a nation to ask another nation if they want to share the map of a region. If the nation accepts, the proposer will, at a cost of -15 prestige, discover all provinces that were not yet discovered in the specific region. The nation giving the map will receive 10. Both nations have to be at peace, and can't be rivals of each other. In order to be able confirm the map exchange, the receiving nation has to have a unit stationed in a region adjacent to the specific region.
The factors that influence an AI nation's willingness to share maps are:
Ask for military access
Request military access from the target country, allowing the requester's land armies to pass through its territories. Acceptance will raise the requester's opinion of the host country by +10, while rejection will decrease it by -10. Declaring war on a country that is granting the aggressor military access causes a major -5 hit to stability.
AI nations will only grant military access if they have more positive than negative reasons for doing so. The relevant factors are
Military access is shared for all participants in a war. For example, if France and Brittany are in a war against Burgundy and France requests military access from Savoy, then Brittany will also have military access to Savoy. Similarly Burgundy, and all of its war allies, would also gain military access to Savoy.
Subject nations always give military access to their overlord. All participants in a war automatically grant military access to their allies, as well as being able to march into their enemies' territory. An army in non-allied land when war is declared, or in territory without military access when war ends, will be exiled.
Offer military access
Offer military access to the target country, allowing their land armies to pass through the requester's territory. Acceptance will raise the target country's opinion of the requester by +10. AI nations are typically uninterested in obtaining military access unless they are the country's ally or subject, or the country is a large and sprawling empire. They will also seek access if they need to travel through a nation to fight in a war. Countries automatically gain military access to countries that grant military access to someone they are at war or allied with.
A country can't revoke access to someone if they, or someone they are at war with, still has troops inside the country's borders.
Ask for fleet basing rights
Acquiring fleet basing rights from a nation will give the following benefits:
- Naval supply range will now extend from the ports of that nation.
- Trading range will now extend from the ports of that nation.
- The requester may dock and repair ships in the ports of that nation.
- The requester may disembark ground troops in that nation by docking loaded transports at its ports. These land troops will not be exiled, and may move into any adjacent province that they would normally be able to enter.
The cost of purchasing fleeting basing rights is as follows:
- The base cost is 0.1 ducats per month per port, with a minimum of 0.5 ducats and maximum of 2.0 ducats. This fee is based on the amount of permanent ports.
- Non-city colony ports are usable and count toward the fee.
- Ports that reside in a province which are terra incognita to the receiving country also count toward the fee.
- Occupied ports only charge a fee if they can be docked at.
- The fee can be seen in the economy window under Harbor Fees.
Fleet basing rights no longer extend colonial range as in past versions of the game. They can still be used to great advantage by distant fleets however. With El Dorado active, they are no longer useful to explorers since they no longer take attrition while exploring. Only nations that have diplomatic technology level 2 or higher can grant fleet basing rights.
The following factors will influence an AI nation's decision to grant fleet basing rights:
Once fleet basing rights have been obtained, AI nations will generally not revoke them unless there is a drastic change in relationship.
Offer fleet basing rights
Some diplomatic actions require control of the Curia and are also discussed on the papacy page. One of the diplomatic actions, call for crusade, allows the curia controller to call a crusade on a heathen nation. This will give every Christian nation bonuses if they are fighting in a war against the crusade target. The other action, excommunication, will grant every neighbor of the excommunicated ruler of a nation a free casus belli.
The Emperor of the Holy Roman Empire has several special diplomatic options available. These action are each explained in more detail on the Holy Roman Empire page.
Great Power actions
- 主条目：Great power
The top 8 high-scoring nations receive the Great Power status. For being a great power, you will unlock the following actions:
- 承担外国债务——偿还目标非列强国家的所有贷款。每笔贷款+10 关系，最多加到+200，每年衰减-2，同时每笔贷款获得+1 信任（无DLC哥萨克）或+2 （有DLC哥萨克）。本国金币需足以偿还目标国所有贷款。
- 影响国家——支付给目标非列强国家该国一年的收入，并在接下来的10年间赠予该国+1 该国最低的一项君主点数。这将在接下来的10年间增加其对本国的+25 关系和+5 信任。与该国交战会移除此加成。
Note: nations who lose the status have access to the above actions for a grace period of 5 years.
These actions are not in the main list, but are also conducted via the Diplomacy panel.
以下内容需要完善：exact criteria for which countries can be set as rivals。
Rivals are countries that a nation expect to come into conflict with in the future. Rivals are usually very comparable in military and diplomatic power and have interests in the same regions and thus will often clash with each other. Rivals may be only selected from countries that are comparable in power. When in the rival selection screen, the nations that are available as rivals and their corresponding opinion of the country and their relative army and navy strength can be seen. A country can have up to 3 rivals at the same time. If a rival becomes too weak or too strong it will cease being a valid rival. When selecting possible rivals, the game will take the relative army strength into higher account than the relative navy strength. Relative development and technology levels are also taken into accord. Nations must be relatively near to be eligible rivals, with more powerful countries able to have rivals at greater distance. Setting a nation as a rival will greatly decrease the amount of diplomacy that can be exchanged between the two nations. Rivals rarely accept diplomatic requests from their nemeses. In order to be rivals both countries must have each other discovered. Selecting a rival has the following benefits:
- A nation is more likely to sign alliances with the enemies of their rivals.
- +25% prestige from defeating a rival in battle.
- No trade efficiency penalty from embargoing the rival.
- +25% spy network build rate against the rival.
- −33% Diplomatic Power cost for demanding unjustified provinces from the rival in peace deals.
Having a rival and taking actions against it grants power projection. Not having enough rivals gives a penalty to power projection.
This releases a country as a vassal. The released country gets all of their core provinces that are owned by the releasing country, except for the releasing country's capital if applicable. Nations can only be released if at least one owned province is both a core of the nation and has its primary culture. This action can not be done while at war.
- See in Static modifiers#Base values). (
- See in : NUM_POSSIBLE_RIVALS = 3,
- See in : RIVAL_PRESTIGE_BONUS = 0.25,
- See in : RIVAL_SPY_OFFENCE = 0.25,
- See in : RIVAL_PEACE_COST_REDUCTION = -0.33,
- See in : CHANGE_RIVAL_YEARS = 25,
- See in : PS_REPLACE_RIVAL = 100,