戦争
Warfare is the most straightforward way of expanding a character's Realm, using your Army to take titles by force. All wars require a Casus belli, which provides a war Objective and consequences for each side winning or losing the war. A character cannot declare war while in Debt.
Warfare
Combat phases
Battles start when two hostile armies enter the same Barony. At the start of any battle, the terrain's Combat Width decides how many troops are able to fight each other at the same time. Each battle goes through 4 phases:
Maneuver Phase: The armies prepare for battle and the Commanders make their initial Advantage rolls.
Early Battle Phase: The armies fight and inflict damage upon each other daily and cannot retreat. If an army is defeated in this phase, all Routed Casualties become Fatal Casualties.
Late Battle Phase: The armies keep fighting and keep inflicting damage upon each other each day until either all soldiers on one side run out of Toughness or one side decides to retreat. If an army retreats, all remaining soldiers become Routed Casualties.
Aftermath Phase: The winning army gives chase to the defeated army and attempts to turn Routed Casualties into Fatal Casualties. When the phase ends, the defeated army moves into an adjacent Barony with all Routed Casualties and cannot be given orders until if finished traveling a couple of Baronies away, but will travel slightly faster than controlled armies.
The advantage modifier
When combat starts, the Advantage, a modifier that lasts the entire battle and increases the damage of all troops on either side, is calculated for both sides. Advantage can come from traits, terrain, buildings or the Martial skill of the Commander. Each Commander will also make a roll every 3 days in an attempt to increase their Advantage, and the roll can be affected by various modifiers and traits. Each point of Advantage increases an army's damage by +2%. Starting Advantage can be affected by the following:
- +30 if army is defending across a strait
- +20 if army is defending across a large river
- +10 if army is defending across a river
- +5 if liege is leading the army
- -10 if realm is in debt
- -10 if army is gathering
- -10 if army is low on supplies
- -25 if army is out of supplies
- -30 if army is attacking across sea
Siege
A Siege takes place when an army attacks a Fortified Holding and outnumbers the Holding's 
Garrison and is the main way of gaining War score. In order to occupy a County, all Fortified Holdings have to be occupied. Castles and County Capitals are all fortified by default. How difficult it is to besiege a Fortified Holding is determined by its 
Fort Level, which can be increased by certain buildings and modifiers. The base amount of Siege Progress needed to occupy the Holding is 100, and each Fort Level increases it by 50. Siege Progress is gained every tick, especially if the attacker heavily outnumbers the garrison or brings siege weapons.
Being attacked while besieging a Fortified Holding will make the besieger the attacker of the battle, conferring any terrain defensive bonus to the other army instead. There is also an additional Advantage penalty for fighting in the same Barony as a Fortified Holding.
Each siege will keep track of the defenders' supplies, average health and fortifications. During sieges, certain events can happen by default every 20 days (shortened by 30% to only 14 days with 
Military Engineer commander), which can lower one of those. Walls can only be damaged if the attacking army has Siege Weapons.
| Asset | Stage 1 effects | Stage 2 effects | Stage 3 effects |
|---|---|---|---|
 Garrison Supplies
|
None |  +10% One-Time Siege Progress
|
+30% One-Time Siege Progress
|
 Garrison Health
|
None | +10% Daily Siege Progress
|
+20% Daily Siege Progress
|
 Walls
|
None |  -10% Time Between Siege Events Can assault the Fort
|
-30% Time Between Siege Events Can assault the Fort
|
Assaulting the Fort will add a large amount of daily Siege Progress at the cost of casualties.
Occupation
Once the besieging forces reach 100% siege progress, they become the controller of the barony. If they control all fortified holdings within a county, they will also occupy the entire county. Upon occupation, the county loses control (unless original owner has the Overseer lifestyle perk Enduring Hardships). Occupying the war target's holdings provides warscore.
War score
War score is a measure of which side is winning a war. It ranges from -100 to +100, each point added to one side being subtracted at the same time from the other side, e.g. if one side has 25 War score, the other side will have -25 War score. War score is gained by winning Battles, occupying Holdings, taking important prisoners and especially having control of the Casus Belli's Objective, or the "War Target". Even though the game doesn't define the term "War Target", it appears to correspond to whether the defender still has possession of at least one county in the de Jure title being fought over. For example, if this is a kingdom level war for England, then as long as any single county in the de Jure England Kingdom belongs to the defender (i.e. has not been successfully sieged), then the defender retains the war target. The bonus for the War Target starts at 0%, but after awhile starts increasing, and the longer the war goes without the attacker taking every county, the bigger it gets, until it can dominate everything else. In some ways, this can be seen as implementing a "war weariness" component for the attacking side, and makes kingdoms much harder to take then duchies or counties.
| Objective | Bonus war score |
|---|---|
| Capturing enemy ruler | +100 |
| Capturing enemy heir | +50 (primary heir) +25 (secondary heir) +10 (tertiary heir) |
| Occupying enemy capital | +10 |
The benefits given by winning battles is based on the size of the losing army relative to its total soldier count. The benefits given by occupying holdings corresponds to a percentage of the total holdings the defender has, both inside and outside the war target. Note that the percentage allocated to winning battles is limited to 50% total, so there is no way to win a war as an attacker without also occupying holdings.
At +30 War score, the winning side can call for White Peace. At +100 War score, the winning side can enforce their demands on the losing side. Alternatively, at -100 War score, the losing side must surrender to the winning side. This can be modified by Peace Acceptance, particularly with the Peacemaker Lifestyle Perk.
Players can always Surrender to the opposing side, ending the war and enforcing the opposing side's demands on themselves. The AI will also eventually surrender to the player when the player has 100 war score, preventing the player from taking additional captives or inflicting additional damage to their realm.
War contribution
Wars where either the attacker or the defender has allies keep track of the percentage of War score that was provided by each ally's armies. When the war ends, a certain amount of 
Gold, 
Prestige or 
Piety is shared among all allies based on their War Contribution.
If a war lasts at least 2 years and one of the allies has 0% War Contribution, it will lose -20 
Opinion with the war leader and have to pay Gold or Prestige or promise to earn War Contribution within a year. Breaking the promise will result in losing a Level of Fame as well as -50 Opinion with the war leader.
Ending wars
Wars can end in two ways: victory for one side and defeat for the other, or with a White Peace.
If the attacker achieves victory, they benefit from the effects of the used Casus Belli. If the defender achieves victory, the attacker is forced to pay a large sum of Gold to the defender and will lose Prestige or Piety.
White Peace can be proposed at any point by one of the two sides and requires the other side to accept it. In case of White Peace, the attacker will lose a small amount of Prestige or Piety.
After a War, the allies of both sides will gain Prestige regardless of who the victor was, based on their Contributions.
When a War ends, the attacker will gain a Truce with the defender for 5 years. If the former attacker declares war again while the Truce is active, they will lose 250 Prestige and one Level of Fame and gain -50 General Opinion for 3 years.
Offensive and defensive wars
An offensive war is one where you are the attacker. Usually, these are wars that you chose to engage in. A defensive war is one where you are the defender.
Alliance
After 6 months have passed since the start of a war, the attacker in an offensive war will start to gain negative Opinion with all Vassals. Every two months afterwards, their Opinion will decrease by -1. After the war is over, the penalty will decay with the same speed. Civil Wars, defensive wars, and Great Holy Wars do not cause Opinion loss. Faiths that have the Warmonger tenet also do not suffer this penalty.
Holy wars
Holy Wars are wars started with one of the Holy War casus belli. Unlike other wars, Rulers of the same Faith as the defending Ruler can join the war without requiring an Alliance. A Ruler targeted by a Holy War gains a character interaction to convert to the attacker's Faith in order to end the war in White Peace at the cost of 100 Piety and 3 Levels of Devotion.
Great holy wars
Great Holy Wars can only be declared by a Head of Faith whose faith has the Warmonger, Armed Pilgrimages or Struggle and Submission tenets and can only target Kingdoms ruled by a character of a different Faith. If victorious, all Titles within the targeted Kingdom are seized and divided between the attackers based on their War Contribution. Great Holy Wars can be Directed or Undirected. Great Holy Wars do not cause Vassal Opinion loss no matter how long they last. A faith must have at least 75% fervor to launch a Great Holy War.
During Great Holy Wars, there is no option for White Peace and capturing and imprisoning the opposing war leader or its Heir will not grant War score. If the attacking Faith wins, its Fervor will decrease by -30 while the defending Faith's Fervor will increased by +25%. If the defending Faith wins, the attacking Faith will lose -25 Fervor.
Rulers who contribute to a Great Holy War and knights in the armies that fight such a war will gain the 
Crusader trait if Christian, 
Mujahid trait if Muslim or 
Warrior of the Faith trait if their Religion is any other. In addition, if the character had the 
Excommunicated trait, it is removed.
Directed great holy wars
Directed Great Holy Wars can be declared by Temporal Heads of Faith. If victorious, the Kingdom is granted to the Head of Faith. Rulers of the same Faith can join forces with the Head of Faith, and based on their War Contribution, may gain Piety or Titles in the conquered Kingdom if victorious.
Undirected great holy wars
Undirected Great Holy Wars can be declared by Spiritual Heads of Faith. When declared, a preparation phase starts, during which Rulers of the attacking and defending Faiths can either donate gold or pledge military support to their side.
Each Undirected Great Holy War will have a War Chest, to which characters of the attacking Faith can donate Gold in order to receive Piety equal to half of the amount donated. Donating significant amounts will also grant bonus Opinion with the Head of Faith. When the preparation phase ends, 20% of the War Chest's value will be divided among all rulers who pledged military support for the attacking Faith. The rest will be divided among all rulers who pledged military support if their Faith wins.
During the preparation phase, characters belonging to the Faith of the attacker or the defender can pledge military support. Characters who pledge military support may gain a share of the War Chest's value and will end all wars against characters who also pledged military support. Characters of the attacking Faith who pledge military support can also choose a Beneficiary, a character of their Dynasty who will receive titles in the targeted Kingdom proportional to their War Contribution. Upon pledging, characters of the attacking Faith will gain Piety and the War Chest will gain Prestige and Piety depending on their Primary Title rank:
| Rank | Piety | War Chest Prestige | War Chest Piety |
|---|---|---|---|
 Baron |
30 | 250 | 75 |
 Count |
60 | 500 | 150 |
 Duke |
90 | 1000 | 300 |
 King |
120 | 1500 | 600 |
 Emperor |
150 | 3000 | 1200 |
A character can withdraw their pledge for military support after making it, but doing so will cause them to lose one Level of Devotion.
In addition, during the preparation phase, characters who pledged military support can spend Piety to change the targeted Kingdom.
Once the Preparation Phase ends, the war starts if the projected attacker strength is not 33% lower than the projected defender strength. If the attackers are victorious, the Kingdom is granted to the attacker that had the highest War Contribution. During both war and the preparation Phase, attackers may donate Gold to the War Chest.
Unlocking Great Holy Wars
Each faith has to unlock the great holy wars before it can declare them. To be eligible, the faith must have the right doctrines, its head must exist and not be imprisoned, there must be at least 35 counties in the world following the faith, and at least ten years must have passed since another faith unlocked great holy wars. Additionally, there are requirements based on year and lost holy sites, according to the table:
| Faith | Minimum year | Condition |
|---|---|---|
| Catholic | 1095 | Top liege of Jerusalem is not Christian |
| Catholic | 1000 | Byzantine emperor or top liege of any of these counties is not Christian: Ankyra, Athens, Constantinople, Corinth |
| Catholic | 800 | The top liege of any of these counties is not Christian: Cologne, Halberstadt, Paris, Provence, Toulouse |
| Catholic | - | Top liege of Rome is not Christian |
| any faith | 1100 | |
| any faith | 800 | Any two holy sites are in a realm whose top liege is not of this religion |
| Islam | - | After Christianity has unlocked, and any holy site is in a realm whose top liege is not Muslim |
| any faith | - | After both Christianity and Islam have unlocked, and any holy site is in a realm whose top liege is not of this religion |
Raiding
Raiding is the process of attacking the Holding of another character without requiring to be at war with them in order to gain Loot. In order to Raid, a ruler must be of either unreformed Pagan religion or Tribal government. Once a Holding has been Raided it cannot be Raided again by the same enemy for 5 years, during which time the Holding will have -50% Taxes, +50% Building Construction Time and -10% Development Growth. If the raided Barony is a Ruler's Realm Capital, raiding may capture or kill courtiers or family members. Holdings that have been Raided will have a torch icon above them when a raider army is selected.
Raiding is done via Raiders, armies raised in owned provinces for the purpose of Raiding that can carry loot based on the army size. Raiders cannot embark unless their culture has unlocked either the Longships or the West African Canoes Innovation. While Raiding, the army cannot move, allowing the attacked character to raise an army against the raiders if possible. If a Raider army is defeated before returning inside its own borders all Loot will be recovered.
If a Commander has raided at least 20 times, each raid has a chance to grant them the 
Raider trait equal to the amount of times they raided.
If the Liege is the army's Commander after the Holding is raided, there is a 30% chance they will gain the option to sack its County. The chance is increased to 50% if the Liege has the Raider trait.
Sacking the County presents at least one, sometimes two options. A player can always sack for additional treasure, granting more Gold and Prestige while the County will gain -40 
Development Progress. When sacking a feudal or clan barony, if one’s capital has under 15 Development, they are also presented with a second option to capture slaves for their capital. Choosing this option will increase Development progress in the raider’s capital by +40, decrease the sacked county’s development by -1, and decrease sacked county’s development progress by -80. Capturing slaves is perhaps the fastest way in the game to increase development, but can only be done in your capital county up to development 15.
Choosing either option will also give the County the Recently Sacked modifier for 20 years, which prevents it from being sacked again and gives it +20 Popular Opinion. Sacking a County will grant +10 
Stress if the character has the 
Compassionate or 
Forgiving traits.
Maintenance cost for armies raised as raiders is reduced by 50%.
Raided rulers gain a decaying -15 Opinion towards the owners of the raiding armies.
Terrain
Each Barony has a dominant terrain. The terrain determines the movement speed and combat width in the Barony and can affect the supply limit and development growth in its County. It may also determine which buildings may be built in a county. There are 14 different terrain types in the game:
| Terrain | Movement Speed |  Combat Width
|
 Defender Advantage
|
 County Supply Limit
|
County Development Growth
|
Other effects | |
|---|---|---|---|---|---|---|---|
 Desert
|
70% | 100% | — | −30% | −50% | — | |
 Desert Mountains
|
50% | 50% | +12 | −60% | −50% | −30% Defender Retreat Losses | |
 Drylands
|
100% | 100% | — | — | −5% | — | |
 Farmlands
|
100% | 100% | — | +50% | +20% | — | |
 Floodplains
|
100% | 75% | — | +35% | +20% | — | |
 Forest
|
80% | 90% | +3 | −10% | — | — | |
 Hills
|
80% | 80% | +5 | −10% | −10% | — | |
 Jungle
|
50% | 70% | +6 | −25% | −40% | — | |
 Mountains
|
50% | 50% | +12 | −50% | −25% | — | |
 Oasis
|
100% | 100% | — | +10% | +10% | — | |
 Plains
|
100% | 100% | — | — | — | — | |
 Steppe
|
100% | 100% | — | — | −50% | — | |
 Taiga
|
80% | 80% | +4 | −20% | −5% | — | |
 Wetlands
|
70% | 60% | +5 | −25% | −25% | +25% Retreat Losses +20% Fatal Casualties | |
References