Subject empire

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This article is for the PC version of Stellaris only.

A subject empire is an Empire that has a special diplomatic relationship with another empire of superior strength. An empire can become a subject either forcefully through wargoals or willingly, though the latter requires both a superior relative power and a positive attitude towards the superior party. In the default galaxy map mode subjects have the same color as their overlord.

If they have fleets available, subject fleets tend to follow the overlord's.

Subject types

  • Diplomacy istributary.png Tributary is the most independent type of subject. The subject pays 25% (35% if the overlord has the Protection Racket tradition) of its mineral and energy income to the overlord, but in turn the overlord is unable to attack it. Neither the overlord nor the Tributary have any obligation to help one another when attacked or attacking and the tributary is free to expand and conquer. If this state is acquired via warfare, a cost free Guarantee of Independence is signed with the Tributary. However this Guarantee can be revoked at any time with the usual penalties. Due to the Guarantee and Subject Relationship, Trust grows quickly up to 100. This state can be converted into a Protectorate or Vassal by conventional rules, with Trust functioning as a significant positive modifier.
  • Diplomacy isprotectorate.png Protectorate is a subject protected by a technologically superior Empire. The protectorate gains a huge research bonus (−80% cost) to all technologies that their overlord has already researched and is automatically converted to a vassal once they researched 50% of the overlord's current tech. Any pre-FTL species that is technologically enlightened is automatically created as a Protectorate under whichever Empire granted them the ability to space-travel. The overlord in turn gains +0.25 Influence.png influence each month. The overlord will defend the protectorate when attacked, but the Protectorate is not drawn into wars unless it turns into a vassal. In addition the protectorate cannot colonize beyond their borders or declare wars. Hovering over the protectorate icon shows how much of the overlord's technology they researched.
    • It is possible for a technologically Superior empire to Offer Protectorate Status to an Inferior neighbouring empire without the Domination Tradition. However, without the Domination Tradition, it is impossible to turn anyone into a Vassal, and therefore a Protectorate will become independent once they have finished researching enough amount of technology. Due to these facts, as either advantageous or disadvantageous, it is possible to Offer Protectorate Status to a hostile empire, to declare a war to subjugate them, and then to integrate them as usual. However there is a risk they may become independent within the 10 years of time required to begin Integration.
  • Diplomacy isvassal.png Vassal is the most controlled type of subject-Empire. They will automatically join their overlord's wars, aggressive and defensive, and they have no autonomy when it comes to foreign policy or diplomatic relations, nor can they colonize new worlds that are outside their border range. If there are significant technological differences between both empires, this option is replaced by the Protectorate status. Planets owned by vassals count towards their overlord's victory conditions. A vassal will contribute with 20% of its Naval Capacity to its overlord, 50% with the Fleet Levies tradition.
    • Demanding Vassalisation requires the Domination Tradition to first be unlocked. Doing so, should the empire reject, grants Casus Belli of Subjugation against it.

Subjects of Awakened Empires

Should a Fallen Empire awaken, they will offer every empire the option to become their subject, sparing an empire their potential wrath.

  • A Satellite is a subject of the Watchful Regulators. They must pay 25% of their Research.png research production to the Fallen Empire, and are forced to outlaw artifical intelligence.
  • A Thrall is a subject of the Jingoistic Reclaimers. They cannot build new starbases and pay 25% of their Mineral and Energy income to the Fallen Empire. However they can declare war and conquer systems from each other.
  • A Signatory is a subject of the Benevolent Interventionists. They have no autonomy over their diplomatic policy and are forbidden from purging or conducting slavery but can expand and the Benevolent Interventionists will come to their protection should they be attacked.
  • A Dominion is a subject of the Doctrinal Enforcers. They must pay 25% of their Mineral and Energy income to the Fallen Empire. Their ethics are changed to Fanatic Spiritualist.png Fanatic Spiritualist, leaving them with only one non-fanatic ethic from the original. Some civics might become invalid, requiring the government to be reformed with more compatible civics when possible. Gestalt consciousness.png Gestalt Consciousness empires do not change ethics however.


A Satrapy is a subject of the Horde. It has to house a Void Dwelling in their capital system (to ensure both their protection and submission) and pay tribute to the Great Khan, but is otherwise left to its own devices and will not be attacked by the Horde. Satrapies have to pay the following:

  • 10% Energy Credits.png Energy Income
  • 20% Minerals.png Minerals Income
  • 30% Mod fleet size add.png Naval Capacity

An empire can only submit as a Satrapy once. If it rebels the Great Khan will not demand subjugation again.

Subject actions

For subject empires the attitude is replaced by loyalty, expressing how content they are living under their Overlord’s rule. If a subject's loyalty becomes low they refuse any deal with the overlord and have a chance to start a war for independence, always waiting for an opportunity when something depletes the overlord's fleet (a taxing war, a larger uprising, a crisis, etc.). The loyalty is determined by the subject's opinion of the Overlord, which aside from the normal factors is also affected by the total military strength of all the subjects relative to the Overlord as well as that of those who support their independence.

An Empire is able to support the independence of another Empire's vassal. Doing this will count the supporting empire's fleet for the relative power of subjects opinion modifier, causing the subject to rebel if they stand a good chance of victory. If they do, the Empire supporting them automatically joins their war for independence. An Empire is also able to guarantee the independence of a smaller Empire, automatically entering the war on their side should they be attacked.

Subject empires do not suffer from border friction and can therefore in some cases be utilized as buffer states between two empires that otherwise would have significant border friction issues.

Subject Actions Modifiers

  • Civic feudal realm.png Feudal Society civic reduces penalty of relative power of subjects in half and allows them to build starbases in unclaimed systems.
  • Tradition domination star lords.png Star Lords tradition provides +20 Diplomacy opinion.png opinion and +50 Trust cap trust cap with subject empires.
  • Tradition domination fleet levies.png Fleet Levies tradition adds Mod fleet size add.png +50% vassal naval capacity contribution (actual contribution is half of vassal's capacity).


Subjects that an empire possess for longer than 3 600 Time days can be peacefully "integrated" by paying Influence.png influence, at a rate of 5 Influence.png influence a month. The base cost is 20, increased by 5 for each pop and 50 for each planet. Only one vassal can be integrated at a time. Both the time before integration and the integration cost can be reduced through Domination traditions.

Once the integration is completed, all planets and ships of the vassal are transferred to the overlord; the ships and starbases retain their graphic type. All leaders, resources and armies are removed; new scientists are required for their science ships.

Empires with the Ap shared destiny.png Shared Destiny ascension perk benefit from a -75% Influence.png influence cost to integrating subjects.

Releasing a vassal

A player can create a vassal from their own territory by releasing one of their systems as a vassal from the "Planet Summary" tab of a planet outside the capital system. This planet becomes the vassal's current capital and the Starbase and every colony in the system are transferred to them. The player can then transfer additional systems to their vassal through the Trade option "Transfer System" if they so choose. Sometimes it is preferable to conquer systems and then release them as a vassal since this will create a vassal that shares the overlord's ethics and government. Notably, the vassal will be granted all its overlord's technology. The option to release a vassal is not available to Determined Exterminators or for species with Culture Shock or the Hive-minded.png Hive-Minded and Nerve Stapled.png Nerve Stapled traits.


For players wishing to utilize subject empires extensively, there are a number of things they can do to maximize their effectiveness. The Domination Menu icon traditions.png Tradition tree contains many helpful bonuses that will increase the benefits provided by subject empires such like increased resource payoffs from Tributaries, more Mod fleet size add.png Naval Capacity from vassals etc. If one wishes to acquire or create subject empires and utilize them extensively, it is highly recommended to adopt and finish the Domination Tradition tree as it provides many benefits for an empire wishing to utilize subject states.

In addition to the Domination Tradition tree, there is also the Civic feudal realm.png Feudal Society Civic which, if an empire has it, will make all of its Vassals more loyal to it as it causes all relation, opinion and trust penalties caused by relative fleet power to be cut in half. In addition to that, it also allows Vassals to build new Starbases and colonize new planets, something that is not possible otherwise. This opens up a lot of options for utilizing Vassals; One could, for example, create a Vassal by releasing a system you own as one and then delegating the task of colonizing worlds to the Vassal while the overlord focuses on their economy, fleet etc. Since the Feudal Society Civic greatly reduces opinion, relation and trust penalties incurred from relative fleet power, the vassal is a lot less likely to rebel and it an be integrated later to allow the overlord to claim the systems that the vassal has colonized.

Alternatively, when starting a new game, one could launch an early war to vassalize one or multiple of their starting neighbors. In the early stages of the game, most empires (aside from Advanced- and Fallen Empires) are still in the process of establishing themselves and are thus likely going to be rather weak economically and militarily, making them relatively easy conquest targets for empires with enough military strength. This is where the Feudal Society Civic comes into play; without it, an empire vassalized early in the game is going to remain at largely the same power level it was at when it was vassalized, effectively stopping its expansion and development. As the game progresses and other empires grow bigger and stronger, empires vassalized early on in their expansion and development will quickly become powerless relative to their neighbors, making them of little use. If an empire has the Feudal Society Civic, however, any empire vassalized by it early in the game will still be permitted to build new Starbases to claim systems and colonize new worlds, allowing it to continue its expansion and development, becoming bigger and stronger along with its overlord. This can allow it to gradually become more powerful, granting a reasonably good mid-game ally for the overlord empire and once the vassal has served its purpose or if it holds valuable planets, it can be integrated by the overlord at their leisure as long as relations are good enough.

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