What is a Great Holy War
Not to be confused with a Holy War, a Great Holy War is War that can only be declared by a Head of Faith. The religion for the Head of Faith does require either the Warmonger, Armed Pilgrimages or Struggle and Submission tenets and can only target Kingdoms ruled by a character of a different Faith. For example the Catholic faith has Armed Pilgrimages tenet and is able to declare a Great Holy War against another faith such as Muwalladi, an Muslim Faith. Great Holy Wars can be either Directed or Undirected. Great Holy Wars are unlike other Wars in the fact that Vassal Opinion does not get negatively impacted, no matter how long they last. Additionally a faith must have at least 75% Fervor to launch a Great Holy War. You can check the Fervor levels by clicking your Religion Icon in the bottom right of your screen by your character.
Unlike other Wars you will not have the option for White Peace and capturing / imprisoning the opposing War Leader or its Heir will not grant War Score. War Score is limited to controlling the Objective, Winning Battles and Controlling Territories. The Capacity for each category is increased to ensure a winner can be achieved. If the attacking Faith wins, its Fervor will decrease by -30 while the defending Faith’s Fervor will be increased by +25. If the defending Faith wins, the attacking Faith will lose -25 Fervor.
Rulers who contribute to the Great Holy War and Knights in their armies that fight in the war will gain a special trait. Crusader trait for Christian faith, Mujahid trait for 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.
Types of Great Holy Wars
The two types again are Directed and Undirected. The main differences are based on the type of Head of Faith, how it begins, and what is won by the participating rulers. There are two types of Heads of Faith. The first is a Temporal Head of Faith, which acts much like a normal Ruler, with the Head of Faith Title being destroyed should they lose all their land. The second is a Spiritual Head of Faith is Theocratic and does not have to be landed, although they can be.
Directed Great Holy Wars
Directed Great Holy Wars can only be declared by Temporal Heads of Faith. The Pope for Catholics would be a Temporal Head of Faith, as they control land under the Papacy. Both Great Holy War types aim to take over a Kingdom Title that is owned by an opposing Faith. In Directed Great Holy Wars the intention is to bring the Kingdom under their own rule. If Victorious the Kingdom will be granted to the Head of Faith and the Rulers of the same Faith that joined forces with the Head of Faith, may gain Piety or Titles in the conquered Kingdom based on their War Contribution.
Undirected Great Holy Wars
Undirected Great Holy Wars can be declared by Spiritual Heads of Faith. When declared there is a preparation phase that begins. During this phase Rulers of the attacking and defending Faiths can either donate gold or pledge military support for their side. Characters of the attacking Faith that donate Gold will receive Piety equal to half the amount donated. Donating a significant amount also grants a bonus Opinion with the Head of Faith.
The pledged support all goes into a pot, which is called the War Chest and 20% of the War Chest’s value will be divided among all Rulers who pledged military support for the attacking phase at the end of the preparation phase. The preparation phase ends and the War starts if the projected attacker strength is not 33% lower than the projected defender strength. For example if the defender has an anticipated 100,000 armies, than the War won’t start until the attacking strength is at least at 68,000 armies. Any lower and preparation will continue. The rest of the gold will be divided among all rulers who pledged military support if their Faith wins.
The last part of an Undirected Great Holy War is the Beneficiary. Every participant in a Great Holy War can select a Beneficiary from their Dynasty that is unlanded. Upon victory the Beneficiary will receive lands in the targeted realm proportional to the War Contribution of their patron ruler. The largest contributor can force their Beneficiary to receive the main title being fought over through the Great Holy War banner in the bottom right of the screen.
Upon pledging support, 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 at the cost of losing one Level of Devotion. The targeted Kingdom can be changed during the preparation phase by characters who pledged military support by spending Piety.
Unlocking Great Holy Wars
Great Holy Wars are not just available at any time and there are certain conditions that need to be met. To be eligible for a Great Holy War, the Faith must have the right doctrines (mentioned at the beginning), its Head of Faith 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. Also, there are requirements based on year and lost Holy Sites. Refer to the table below for these requirements:
| 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 |