The Imperium of Man is a war-torn empire, teetering on the brink of collapse. For ten thousand years is has been ruled by the deathless Emperor, a being of incredible power, to whom thousands of souls are sacrificed daily. The peoples of the Imperium live in a place where Daemons are real, mutation is frequent and death is a constant companion.
A truly vast domain, the Imperium is spread amongst the many stars of the galaxy. Its territories encompass untold millions of stars and countless more human lives. In its name, terrible wars are fought and desperate sacrifices made, yet even this river of carnage and blood is a small price to pay, for the Imperium is the guardian of mankind. Were it to pass into nothingness, so too would the human race, destroyed by enemies uncountable, to the laughter of the Dark gods.
The Imperium covers a wide area of galactic space, sprawling over countless worlds. There are few universals amongst these varying planets. Culture, language, and even the human form appear in seemingly infinite variation across the universe. One of the few constants (at least amongst those worlds of the Imperium that are aware of its existence) is the network of feudal obligation and responsibility.
Each Imperial planet owes fealty to a planetary governor. This individual in turn renders to the Imperium’s priesthood a tithe of men, materials and loyalty. The governor is also expected to reject enemies of the Imperium, and to ensure that the psykers upon his planet do not fall into witchery or possession. In return, the governor can call upon the priesthood (or Adeptus Terra as they are properly known) in times of dire threat and request aid.
The Adeptus Terra comprises a bewildering variety of departments, bureaus, sub-divisions and offices, each of which deal with a particular aspect of maintaining the continuity of the Imperium. Each order has an obligation to care for its given area of control.