Hello everyone, and welcome to another Development Diary for Europa Universalis V!
Over the past six diaries, we’ve journeyed through the core pillars that define EU5: from the intricacies of population mechanics, to government and economy, exploration and colonization, religion and culture, and finally military. Each of these systems lays the foundation for the next generation of grand strategy.
But today, we turn our focus to something even more delicate and equally powerful: Diplomacy, the art of managing relationships between nations.
While wars may shape borders, diplomacy defines the world that emerges from them. So let's get right into it.
“To hold a pen is to be at war.” And nowhere is that truer than within the Holy Roman Empire, where 312 states exist in a constant web of alliances, rivalries, and imperial politics. In such a landscape, the pen often proves mightier and potentially far more dangerous than the sword.
Diplomacy Basics
To begin we will start with the Diplomats system within EU5.
In our previous Europa Universalis title, diplomacy relied on a fixed number of diplomats, each capable of performing one action at a time. In EU5 this system of diplomats has been reworked. Diplomats now function as a form of diplomatic currency, representing how much diplomatic activity your nation can sustain at any given time.
Every diplomatic action, whether it’s forming an alliance, proposing a royal marriage, or declaring war will require spending a diplomat. While ongoing diplomatic actions such as improving relations, currying favors, or building a spy network will require a monthly diplomat cost.
The number of diplomats and generation of new diplomats varies depending on country rank, societal values, advances, diplomatic spending and building the Royal Garden building in your capital.
Starting diplomats and diplomatic generation of Upper Bavaria, the emperor of the HRE in 1337.
Another key element shaping international diplomacy is Diplomatic range, the measure of how far your diplomats can reach beyond your borders.
As the game progresses, your Diplomatic Range expands through advances and upgrading country rank (i.e Duchy versus Kingdom). This value determines the maximum physical distance your diplomats can travel to conduct diplomacy, calculated by the distance between the capitals of the two nations involved.
In the early game, the diplomatic range is similar to what nations can see. For example England in the start date will be able to diplomatically interact with the Golden Horde, Morocco, Mamluks or Georgia but will be unable to diplomatically interact with Yemen.
Although England in 1337 can interact with the Mamluks, Yemen is out of their diplomatic range.
Foreign envoys is an advance in the Age of Renaissance that increases diplomatic range by 33%.
Once you have begun forging alliances, creating subjects, or joining some international organizations, another vital mechanic comes into play: Diplomatic Capacity.
Diplomatic Capacity represents the extent of your nation’s diplomatic commitments, determining how many formal relationships your state can actively maintain at one time. But not all relationships are equal. Stronger allies and larger vassals will cost more in terms of diplomatic capacity usage. An alliance with France will be much more costly than alliance with the county of Ulm, a large fiefdom will be more costly than a small vassal. You can go over this diplomatic capacity limit but it will cost you in diplomatic reputation and prestige.
Diplomatic capacity increases with country rank, advances, diplomatic spending and building the embassy building in other nation’s capitals.
Careful on who you choose to ally and how big your vassals get, you might find yourself overwhelmed in your diplomatic endeavors.
In Europa Universalis V, you can invest directly in diplomacy through the Diplomatic Spending slider found in the Economy tab.
Increasing your spending boosts subject loyalty, diplomatic capacity, the maximum number of diplomats, and your monthly diplomat generation. How much you invest depends on your strategy, sometimes saving ducats for wars or building is wiser, while other times, investing heavily in diplomacy can secure alliances and maintain subjects.
Diplomatic Reputation returns in EU5, now closely tied to the Trust mechanic between nations. Your country’s Diplomatic Reputation represents how highly regarded it is in international relations, particularly it affects how nations view you in terms of reliability. This reliability is represented through the Trust between two nations. Trust measures how confident one country views your nation in acting honorably, whether it's maintaining alliances, honoring treaties, or keeping promises.
Diplomatic reputation is a flat country modifier, increased through advances, laws, government reforms, and national values. Meanwhile trust is a value that varies from country to country, starting at a base level depending on your diplomatic reputation and then impacted by your actions throughout your campaign. You can also increase trust with a nation by professing trust to them, heavily increasing the trust between your two nations at the cost of diplomatic reputation. Increasing trust will greatly impact a nation’s chance of acceptance of alliances, royal marriages and diplomatic subjugation.
The Diplomatic Traditions government reform is an early game reform that can be used to increase your Diplomatic Reputation. A wise choice for the diplomatic player.
The Great Power with the highest diplomatic reputation will become the diplomatic hegemon starting in the Age of Discovery. Being the Diplomatic Hegemon gives a new diplomatic action, Influence Country, allowing you to simultaneously improve relations and trust over time.
Throughout your campaign, you may find yourself in need of money, looking to improve cultural opinion, in need of pops from other nations or aiming to isolate an ally from your rivals. All these diplomatic maneuvers rely on Favors.
You can curry favors with other nations, with the rate of accumulation depending on your Cultural Influence compared to their Cultural Tradition. However, use them wisely, every favor you spend grants that nation favors on you in return. If they later call in those favors and you refuse, your Trust with them will take a major hit.
Favors between two nations are mutually capped, meaning the total of what you owe and what they owe cannot exceed a set limit. Overusing favors can therefore prevent you from gaining more until the balance shifts.
Currying favors with the right nation can change your campaign greatly as a minor power, use them wisely.
Royal Marriages are no longer just a diplomatic action in EU5 and do not cost diplomatic capacity. Instead, they represent a direct union between characters of two royal families. Forming a royal marriage will strengthen trust and relations between nations, but it also carries the potential for dynastic claims. Over time, these ties can evolve into Personal Unions under a Union International Organization, where one crown inherits control over the other’s nation. We will go into more detail on the Union International Organization later in this development diary.
This finally leads to Rivals, countries can declare their hostility towards other countries by declaring them as Rivals. Countries that are declared rivals unlock additional hostile actions against them, like the ability to intervene in wars or the ability to fabricate Humiliation wars, which allows you to heavily reduce your rival’s prestige and increase yours. Choosing a rival also comes with huge negative opinion and removing the ability to do certain diplomatic options.
Who you decide to rival will greatly impact your diplomatic landscape.
Subjects
In EU5 there are multiple types of subjects, the five main types are:
Tributaries: a country that is forced to pay a period tribute to their overlord in the forms of Ducats, Manpower, and Sailors. Tributes can declare their own wars or even declare war on another tributary. They may join their overlord’s wars but it is not guaranteed and is the choice of the subject. This tributary gets protection from their overlord in return. Tributaries cannot be diplomatically annexed by their overlords.
Colonial Subjects: a subject centered around the administration of overseas colonies on behalf of its overlord. They benefit from increased population capacity, institution spread from their overlord, and the ability to use slaves to work in their R.G.Os even if their religion does not allow it. These subjects grant their overlord an upsurge of Trade Advantage as well as payment in manpower, sailors and ducats. They will join their overlord’s offensive and defensive wars. These subjects cannot be diplomatically annexed.
Dominions: a subject nation that is a self-governed subject exclusive for Monarchies who have the same religious group, nations with the same primary culture, nations with kindred cultures, or for the nations of England or Great Britain. This subject enjoys an increase in their Efficiency of Cabinet and outside of England/Great Britain can only be made when nations are already in a Union International organization with each other. These subjects always join both defensive and offensive wars and can be diplomatically annexed after 100 years.
Vassals: the most typical type of subject, a Vassal oversees its territory on behalf of its overlord, paying a vassal fee. Overlords benefit from vassals in terms of prestige increase compared to other subject types and giving both nations, the subject and overlord, better shared institutions. Vassals will always join both defensive and offensive wars but when disloyal can be separately peaced out of wars. They can also declare independence through an independence war if they are disloyal for long periods of times, maybe even allying with other disloyal Vassals. Vassals can be diplomatically annexed after 10 years.
Fiefdoms: are a junior title that is the property of its Overlord’s ruler. Exclusive for monarchies of the same religious group of one another, these subjects differ from vassals in that they have more loyalty and cannot directly declare independence. However they come at a much larger diplomatic capacity cost than vassals and do not share institutions with their overlord. Fiefdoms can be diplomatically annexed after 10 years.
You can directly interact with any of your subjects diplomatically but also can interact with them using the manage subjects interaction screen under the diplomatic tab. Allowing you to see all subjects’ loyalty, opinion and liberty desire and allowing you to choose their military stance from the choice of Normal, Aggressive, Supportive, Passive and Defensive.
How you manage your subjects is a strategic choice, many options are available to you whether you want your subject to attach to your armies (supportive) or focus on defending territory (defensive).
This does not include region unique subjects, available to only some nations in EU5 such as the Indian Samanta, the French Appange, or the Middle Kingdom Tǔsī subjects. These are just some of the unique subjects that you will see while playing EU5. Each with their own abilities, bonuses and setbacks.
Great Yuan Starts with 125 subjects, from Tǔsī subjects, standard vassals to autonomous tributaries.
Every subject has a subject loyalty towards their overlord. Ranging from 0 to 100, once it is below 50 the subject will become a disloyal subject. Disloyal subjects will not aid in wars, only protecting their own land, can be separately peaced out and cannot be diplomatically annexed. Loyalty of subjects can be increased with trust, diplomatic reputation, and improved relations. While loyalty can be decreased by liberty desire, your subjects being more powerful than you and negative relations. Playing as a subject nation you can use a cabinet action to reduce loyalty to your overlord with the sow disloyalty cabinet action.
Liberty desire represents a subject’s current drive for independence from its Overlord. This value ranges from -100 to +100 but it has a monthly decay towards 0. Liberty desire can also be used as a subject currency, with some actions such as enforcing culture, diverting trade or siphoning their income costing Liberty Desire.
Rightfully ‘repurposing’ your subject’s income costs at a cost of 20 liberty desire.
For some subjects, you may want to integrate them eventually. Different subjects will need more time to begin the integration process but all subjects will need 190 opinion to start integrating and above 125 relations must be maintained while doing the integration process. Diplomatically annexing a subject will cost 0.10 diplomats monthly and the speed in which you integrate them varies depending on how many cities, towns, rural settlement locations they have, with cities and towns costing more Diplomatic Annexation cost than rural locations. The Diplomatic annexation process can be further increased by having the same primary culture as your vassal, having higher cultural influence than your subject’s cultural tradition, being much bigger than your subject, and advances.
Integrating this Jaunpur subject with 14 million pops and 41 cities is going to take some time....
Personal Unions are no longer considered subjects but instead an international organization, which we will cover later in this development diary.
Casus Belli
But what is diplomacy without its breaking points, sometimes the option left for a country in EU5 is to declare war. This is where creating and using a Casus Belli (or CB for short) comes into play.
The option to create spy networks at the cost of diplomats is there allowing you to create certain CBs but usually none of the CBs you can make before the age of Revolutions will be that potent for conquest.
For the most part, your parliament will have to be used to make a CB through the ‘Prepare for War Action’ at the cost of 50% parliamentary support.
The ‘Prepare for War’ Parliament action will be the primary way to create conquest CBs before the Age of Revolutions.
Outside of parliament, you can get events or use certain situation actions to get claims for conquest.
The Rise of the Turks situation has an available action for the strongest Turkish Beylik, allowing them to create CBs at the cost of ducats.
Besides conquest, other CBs can be made using a spy network. These CBs range from disrupting trade, humiliating a rival, declaring on an excommunicated ruler, or dealing with piracy. Each CB comes with a war goal and bonuses to war score depending on certain objectives such as winning naval or land battles.
In the Age of Revolutions in 1737, the Imperialism CB is unlocked. Allowing you to create wars of conquest using a spy network. This CB varies to a normal conquest CB in that it reduces war score cost, allowing you to take huge swaths of land from a single peace deal.
Time to take conquest to a whole new level
Unless you are in an international organization like the Holy Roman Empire, the option to declare war without a CB is possible, costing some stability and Antagonism gain.
What CBs you use in your wars will shape your peace deals and how you generate warscore, so remember to choose wisely.
Antagonism
After completing your first war of conquest, you may notice a value known as Antagonism. Antagonism is how negatively other nations view you in your campaign. Countries with high Antagonism toward you will be less inclined to engage in diplomacy and may even act against your interest or join against you in wars.
Unlike Aggressive expansion in EU4, antagonism is not just a value that is caused by aggressive action such as taking land in war. Any nation can have a base level of antagonism towards you based on differences of societal values, government types, religion, culture and language.
In 1337, the Byzantines start with antagonism with the Ottomans
Some actions can also cause an Antagonism ‘bomb’ in a location that affects the countries near it varying degrees depending on how much they care about that location and about the antonizer country. Examples of antagonism ‘bombs’ are conquering land, subjugating through war, events, or executing prisoners.
Over time Antagonism ‘bombs’ will generally dissipate. You can also decrease a nation’s antagonism towards you by improving relations.
I think this is going to cause some issues
In the worst case, nations with over 50 Antagonism will start and join a coalition international organization against you. These coalitions will fire if the coalition feels they are stronger than you militarily and will defend one another if one is attacked by the coalition target.
I think I took too much land
International Organizations
In EU5, nations can band together in some kind of agreement or organization, these groups of nations form what we call International Organizations (IO for short).
There are multiple types of International Organizations varying in size from 2 nations to over 500 nations, with some in the start of the game such as the Holy Roman Empire and the Japanese Shogunate and others forming as the game progresses such as Crusades, the Guelphs and Ghibellines and coalitions.
The Japanese Shogunate International Organization starts with 146 members in EU5’s start date.
Some of these international organizations will have laws that impact all the members or gameplay rules such as the HRE’s internal rule of no no-CB wars that shape the organization as a whole.
International organizations for the most part will have a leading nation, this nation has the authority to start the process of enacting laws or kicking out members; however there are many cases where the leader of the international organization will need either approval of other members through a voting system or International organization value to do actions within the IO (or both). International Organization values differ from organization to organization, sometimes representing the authority of the leader of the IO, like in the Holy Roman Empire. In other international organizations like a Religious Sect IO, the Value represents the influence of the International Organization itself.
A consistent leader of the HRE with high Imperial authority can eventually unite it using the HRE international Organization laws
The Illkhanate International Organization starts with no leader, giving the opportunity to a nation to rise and take the leader role.
This brings us to Personal Unions and the Union International Organization.
When a ruler governs multiple nations, those nations form a Union IO. This IO is a shared political structure led by a single ruler (or a marriage of rulers) who holds the crowns. While Unions primarily act as defensive alliances, they can also cooperate in offensive wars if members approve such actions through the Union Law voting system.
Each law within a Union IO must pass by majority vote among its members. These laws can shape the union’s nature, from its foundation to the pivotal Question of Unification, where the senior partner may begin integrating the junior members. Unification requires a 50-year-old union and follows a process similar to integrating subjects, as discussed earlier.
In order to diplomatically annex junior members, the junior member must have the same level of integration as the senior member and the Question of Unification must be passed for unifying the crowns.
If a new member enters a Union IO years after the original formation of the union, the union parliament can be used to get them on the same level of integration as the senior member.
However, Union IOs aren’t solely about unification. Some may evolve into federal unions, emphasizing equality among members and granting shared bonuses such as improved diplomacy, greater diplomatic capacity, enhanced cabinet efficiency and more.
Over time, the Senior member may diplomatically subjugate smaller ones, turning them into dominions, vassals, or fiefdoms depending on their size. Allowing integration outside the traditional unification path in the union IO.
Belligerent vs Conciliatory Values
To finish this development diary we will discuss a value bar that you should consider while playing. This value bar is the Belligerent versus the Conciliatory values.
On one end of the spectrum, being a Belligerent nation will reduce Antagonism received, decrease warscore cost, increase spy network speed, and increase CB generation speed but at the cost of Diplomatic Reputation.
On the other end of the spectrum, being a Conciliatory nation will increase cabinet efficiency, boost loyalty of subjects, and improve your diplomatic reputation at the cost of Antagonism gain and longer CB generation speed.
You may find that in some campaigns, ignoring the opinions of others and expanding through conquest suits your ambitions best. In others, the power of diplomacy, forging alliances and subjugating nations through negotiation rather than war, may prove the wiser path to greatness.
Belligerent or Conicillatory, the choice is yours….
Diplomacy in Europa Universalis V is far more than a series of actions. It’s a living system of relationships, trust, and influence that shapes the fate of empires. Whether you rule through strength of arms or the subtle art of negotiation, every choice you make will ripple across the world stage. Will your nation rise through conquest, or thrive through compromise and alliance? The balance between war and words is yours to command.
That wraps up our look at diplomacy in Europa Universalis V, if you haven’t already, check out the accompanying feature video here: (link)
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Until next time !