An Imperial Crusade is the term used by the Imperium of Man for a large-scale military campaign organised in order to conquer or retake multiple worlds or an entire sector or sectors of the galaxy. Crusades are usually very large-scale offensives that require a major mobilisation of Imperial military resources across multiple planets and often are fought as a series of smaller campaigns or salients across the chosen theatre of operations. The very first Imperial Crusade, from which the term is drawn, was the Great Crusade led by the Emperor of Mankind Himself from Terra beginning in ca. 798.M30 that lasted for over two hundred standard years and forged the Imperium itself.
Because of the sheer size and ambition of most Crusades, they often require the deployment of forces from more than one branch of the Imperial military, and so are usually led by an Imperial general officer granted the special rank of Warmaster or one with a rank equivalent to that of a Lord General Militant in the Astra Militarum.
An Imperial Crusade can only be declared by a decree of the High Lords of Terra or the Lord Commander of the Imperium and can include any Imperial campaign that is considered either of great strategic importance to the continued health of the Emperor's realm or an offensive unusually broad in scope that will include multiple worlds and last for several Terran years. However, the High Lords have also declared relatively short-lived offensives to be Crusades that were resolved with only a single battle involving small numbers of troops when the objectives were considered to be of particular strategic or political importance.
The declaration of a Crusade is one of the means utilised by the post-Horus Heresy Imperium to unleash an offensive involving multiple different Chapters of the Adeptus Astartes and binding them into a single force similar to the Space Marine Legions of old. In this way, the resources of an entire Chapter do not have to be committed to a single campaign nor do the ponderous gears of the Astra Militarum have to be set into motion, which could greatly delay the Imperial military response when time is of the essence.
Imperial Crusades can also be declared against High Lords considered heretical or even Planetary Governors who have rebelled against the authority of the Emperor. Crusades have also been launched against xenos worlds or human-settled planets that have been newly discovered to lie beyond the Emperor's light.
Imperial Crusades and the Adeptus Astartes
For the Adeptus Astartes, the contribution of Space Marine forces to an Imperial Crusade is often a matter of honour for which they might deploy a squad or two of Astartes when they are called on to lend aid. If the Crusade proves victorious, the Chapter will add that Crusade's battle honour to their Chapter and company standards as a mark of their achievement and loyalty to the Emperor.
Entire Chapters have been known to begin so-called "penitent" Crusades on their own which can last for a full Terran century during which time they are denied the right to take new recruits to replace their losses and their Chapter homeworld is often removed from their administration. Such Crusades are undertaken, as the name suggests, as an act of penance for a perceived failure on their part or as the result of an action the Chapter took that was seen as displeasing to the Emperor. For instance, after the Badab War, both the Lamenters and Executioners Chapters were ordered to undertake penitential Crusades as a punishment for their service to the Secessionists' cause during that conflict.
Such a punishment is levelled only for acts considered violations of the Emperor's trust but not so malignant as to earn the designation of Excommunicate Traitoris -- a true Traitor to His will. Penitent Crusades are willingly undertaken by Astartes Chapters deemed to have dishonoured themselves as their completion earns both the forgiveness of the Emperor and the restoration of the Chapter's former privileges, their homeworld, and the right to recruit Aspirants.
Among the Adeptus Astartes, the Black Templars are known to have embarked upon a single, eternal Imperial Crusade since their Founding. The Chapter is fleet-based and its forces are scattered across the galaxy fighting in myriad different conflicts, each of which is a separate Crusade that is considered to be just one part of their broader mission to Crusade against the Emperor's enemies. A "Crusade" is also the term used by the Black Templars to designate the primary organisational unit of their forces, with each Crusade essentially serving the role of a traditional Astartes company as outlined in the Codex Astartes for standard Chapters.
In mockery of the Imperium and the Great Crusade which created it, the servants of Chaos call their major incursions into realspace "Black Crusades." The thirteen Black Crusades led by Abaddon the Despoiler, the "Warmaster of Chaos," have proven to be some of the most dangerous and potent military threats the Imperium has ever faced.
Notable Imperial Crusades
- 519th Crusade
- Abyssal Crusade
- Achilus Crusade
- Aegisine Crusade
- Second Aegisine Crusade
- Ajaxian Crusade
- Altid Crusade
- Angevin Crusade
- Arkron Crusade
- Bellrath Crusade
- Blackfang Crusade
- Bloodswarm Crusade
- Children's Crusade (the Lost Crusade)
- Corinthian Crusade
- Crusade of Fire
- Dark Marches Crusade
- Damocles Crusade
- Declates Crusade
- Geonide Crusade
- Ghoul Stars Crusade
- Great Crusade
- Helican Crusade
- Helsreach Crusade
- Hive Thetus Crusade
- Indomitus Crusade
- Jerulas Crusade
- Macharian Crusade
- Margin Crusade
- Mephistari Crusade
- Nightfire Crusade
- Nimbosa Crusade
- Omniel Crusade
- Crusade of the Ophidium Gulf
- Palatine Crusade
- Proletarian Crusade
- Sabbat Worlds Crusade
- Saint-Saen Crusade
- Second Abonian Genocide
- Skarath Crusade
- Terran Crusade (M41)
- Terran Crusade (M36 - Wars of Apostasy)
- Thangdron Crusade
- Thorados Crusade
- Ullanor Crusade
- Vinculus Crusade
- Codex Adeptus Astartes - Blood Angels (7th Edition) (Digital Edition), "A Chronicle of Heroes"
- Codex Adeptus Astartes Supplement: Angels of Death (7th Edition), pg. 30
- Codex: Dark Angels (4th Edition), pg. 19
- Codex: Space Marines (6th Edition), pg. 38
- Codex: Tau Empire (6th Edition), pp. 13, 28-29, 34, 41, 52
- Codex: Ultramarines (2nd Edition), pg. 59
- Deathwatch: The Flesh of the Angel (Short Story) by Ben Counter
- Imperial Armour - Imperial Vehicles for Warhammer 40,000, pg. 38
- Imperial Armour Volume One - Imperial Guard and Imperial Navy, pg. 159
- Imperial Armour Volume Two - Space Marines and Forces of the Inquisition, pg. 223
- Imperial Armour Volume Ten - The Badab War - Part Two, pp. 97-98
- Warhammer 40,000: Rulebook (8th Edition), pg. 50
- White Dwarf 405 (UK), "Battle Report: And They Shall Know No Fear"