A War of Assassins is a limited form of warfare that was permitted under the Great Convention and the Guild Peace during the time of the Corrinos. It described a large-scale use of professional assassins in a feud between two great houses of the Landsraad in the Old Imperium.
Atomic weapons were outlawed by the Great Convention and shields nullified projectile weapons and nonnuclear explosives. Hence the Great Houses were obliged to resort to treachery and professional assassination in order to carry on their perennial vendettas.
Formal declarations of intent were required to be filed with the Imperial Court, the offices of the Guild, and the Secretary of the Landsraad. Imperial judges were appointed to monitor the conflict and particularly to observe any instances where innocent bystanders might be harmed. Such actions did not always ensure the safety of noncombatants, nor a fair treatment of the two houses involved, for the emperor was seldom completely disinterested in the conflict. But the observation made the feuding houses wary of harming or even involving outsiders.
Additionally, it permitted only certain kinds of weapons and practices, as outlined in the Assassin's Handbook. These rules were put in place to protect innocent bystanders.
All Great Houses customarily hired a master assassin — usually one with Mentat training in logic and the traditional Mentat distrust of emotion — to oversee the defenses of the family household, supervise the house's corps of assassins, and in some cases to command units of troops or mercenaries. Their function was therefore both offensive and defensive.
Consequently a war often took on the appearance of a Cheops game between two grand masters. However, some great barons or dukes, like Duke Leto I Atreides, although relying on the advice of their chief assassin, may be said to have managed — or mismanaged — their own campaigns.
It's notable that effects of wars of assassins entered the folklore of the Imperium. An expression for someone notorious for his rationality was being "logical as an assassin." And the hour before dawn when human biocycles are customarily at a low ebb was often called the "hour of assassins" because of the tendency of professional assassins to use it for their attacks.
Numerous famous wars of assassins occurred in Imperial history, often altering the balance of power among the Great Houses of the Landsraad. The important wars of assassins dominated political history of the last century of the pre-Atreides Imperium.
- Harkonnen vs Pardee (3367 AG-3375 AG); the first recorded instance of a war of assassins after which House Pardee was virtually obliterated.
- Choi vs Dwyer vs Ferguson war (8787 AG-8843 AG), a three-cornered bloodbath from which each house emerged weakened and ended only when the emperor Jaunvarai II himself interceded with the families in conflict.
- Moritani vs Ginaz (10175 AG-10181 AG); marked total defeat of the Ginaz; Shaddam IV aided the Moritani because of Ginaz's alliance with the Atreides.
- Harkonnen vs Atreides (10191 AG); the largest one in recorded history with the most sweeping political consequences. Harkonnens (under Shaddam's favor) used Dr. Wellington Yueh to cut off the power and lower the shield defenses of the Atreides palace which was overrun by Harkonnen mercenaries and Imperial Sardaukar. Pieter de Vries was the Mentat-Assassin. Casualties were Duke Leto, Yueh, de Vries, Idaho and Liet-Kynes. The Atreides Mentat-Assassin, Thufir Hawate went over to the Harkonnens after their victory.
Although Alia employed numerous assassins, she did not declare any wars of assassination, for obvious reasons. During Emperor Leto II Atreides's long rule, wars of assassins were virtually proscribed, although technically the Great Convention remained in effect. The profession of assassin fell into some disrepute, and those who took up the craft were largely second-rate. The best assassins were the gholas of Idaho with numerous frustrated assassination attempts, most of them directed at the Emperor Leto. Siona Atreides managed to destroy Leto has been seen by some students of political assassination as a victory for amateurs.