The Milky Way Galaxy in the late 41st Millennium AD

　　The Imperium of Man is home to over 1,000,000 human-settled planets scattered across over 100,000 light years of space in the Milky Way Galaxy. Most of these worlds were settled by humans many centuries before the Great Crusade of the 31st Millennium reunited the human colony planets beneath the rulership of the Emperor of Mankind, though thousands more have been settled in the ten millennia since then by Imperial colonists. The Adeptus Administratum of the Imperium generally classifies all planets in the galaxy according to the following classifications for the purposes of raising tithes of raw materials, manufactured products and Imperial Guard regiments.

　　The Imperium of Man is spread impossibly thin across an estimated two-thirds of the entire Milky Way Galaxy. The volume of space claimed in the name of the Emperor of Mankind contains hundreds of millions of stars, many host to their own planetary systems, and yet there are only an estimated million or so Planetary Governors occupying the thrones of the Imperium’s worlds. While it is true that some governors rule not just a single planet but an entire star system, and that other worlds have no governor at all, the fact is that the Imperium is stretched so thinly across the void that an interstellar traveller could make his way from one edge to the other, traversing a hundred thousand light years of space, and not once cross paths with a human being.

　　Instead of being scattered at random, the worlds of the Imperium are clustered around areas settled during the lost age of Mankind’s first great wave of expansion into the galaxy during the Age of Technology. Worlds once colonised because of their location or some desirable natural resource have developed into the cores of sectors, many of which have swollen to include two hundred or more star systems. These sectors are connected to one another by relatively stable, if still hazardous, inter-sector Warp routes and the vast, uncharted reaches between each are referred to as Wilderness Space. These unexplored depths harbour all many of terrors, from ravening pirates to unknown alien empires, as well as untold riches, from long-lost human colonies to worlds strewn with the wealth of long-extinct xenos species.

　　The Imperium encompasses countless worlds. No one has ever been able to map all of them and no one can truly even say how many there are beyond the figure of 1,000,000 normally cited above. Entire departments of the Adeptus Administratum are devoted to cataloguing the worlds in the Emperor’s domains, a never-ending task, for it is in a state of eternal flux. Furthermore, the Adeptus Terra holds that the whole human race and the entire galaxy are under the Emperor’s rule—the Imperium has a Manifest Destiny to unite Mankind, impose its laws on every human world and destroy all alien forms of intelligent life. The true scope of the Imperium is, therefore, the entire galaxy, though this is far from actuality. The Imperium jealously guards its territory whenever it can but its sheer size means that it cannot react to every circumstance. Many planets live and die alone, with only the truly great threats commanding the attention of the Adeptus Terra. Worlds are frequently lost to aliens, rebellion or disasters, with news of their destruction sometimes taking centuries to reach Terra. The Imperium’s borders undergo constant change, with new worlds discovered, conquered or colonised and old ones lost to xenos invasion, Exterminatus, daemonic incursion or even to the Warp itself.

　　The galaxy teems with worlds. The majority are gas giants, worlds of frozen methane, huge, globular masses of hydrogen that failed to become stars, and many other variations. Some of these are mined or exploited in some way and may even harbour their own forms of truly bizarre alien life, but it is mostly upon small, rocky, terrestrial worlds that Mankind, and its enemies, are found. Within this category of world, however, are many variations and humanity endures all manner of different environments in its quest to survive in a cruel and unwelcoming universe.

　　Types of Planets

　　Feudal Worlds

　　Feudal Worlds are planets into which the Imperium has not seen fit to introduce most modern technology, although the advent of certain advanced medical technologies such as basic antiseptic agents is often an exception so as to keep such worlds' labour productivity high in the face of the odd plague or epidemic. Feudal Worlds are defined as those planets of the Imperium that have developed late Iron Age civilisations that are moderately technologically advanced while still remaining pre-industrial, having usually progressed as far as to discover or re-discover rudimentary gunpowder weapons. These planets often possess widespread and advanced farming economies and typically have a population of 10,000,000 to 500,000,000 people. Feudal Worlds are similar culturally and technologically to Terran societies in the Late Middle Ages or Renaissance periods of the Age of Progress. Generally, Feudal Worlds will have little direct political or economic interference from the Imperium and be required to pay only low planetary tithes. Imperial Planetary Governors of Feudal Worlds will generally live on a space station in orbit of the planet to avoid altering the cultural balance, only descending to the surface to deal with heresy, rebellion or rampant mutation. These planets are populated by folk who have lost access to all but the most basic of technologies and maintain Iron Age or early Gunpowder Age societies. Farming, simple labour-intensive machines such as pulleys, windmills and the like are known, but propelled flight, automatic weaponry and powered vehicles are likely to be rare or non-existent. These worlds are often said to be the most politically harmonious of all the planets of the Imperium, because their peoples know their place.

　　For examples see: Fervious, Sisk

　　Feral Worlds

　　Feral Worlds are defined as planets whose population are composed of nomadic hunter-gatherers or members of early agricultural societies and who possess technology equivalent to Old Earth's Stone Age, Bronze Age or early Iron Age cultures. Feral Worlds are populated by tribal peoples largely living without the assistance of maintained technology or even agriculture in some cases and the population is usually quite low as a result, ranging from 100,000 to 5,000,000 people. This may be due to an ancient failed human colonisation project from the Dark Age of Technology, ingrained religious preferences, cultural choice, harshness of the environment or some other reason. Feral Worlds, like their Feudal counterparts, will have little direct political or economic interference from the Imperium and will pay only the lowest grades of planetary tithes, their tithe grade being Solutio Tertius. Feral World populations may be aware of the Imperium's existence in some fashion but are unlikely to know much more than something about a large group of distant people living among the stars. These planets are frequently unsuitable for later Imperial colonisation, either due to the circumstances which drove the natives feral or because the natives themselves actively resist new people settling on their lands. The people of Feral Worlds can range widely in culture, from Grox-hunting Stone Age tribes of ancestor worshipers who only recognize the Emperor of Mankind in the most rudimentary of ways, to wild-eyed, post-apocalyptic road warriors, fighting endlessly amongst.

　　Like all Imperial worlds, Feral Worlds are ruled over by a Planetary Governor, although the nature of Feral Worlds makes this position somewhat different from that of the Governorship of more advanced planets. The Imperial Governor of a Feral World almost always lives apart from the natives, often living in a single city inhabited by outsiders or taking residence in orbit on an Imperial space station, only interfering in the world's affairs to keep psyker and mutant "head counts" down. Religious heresy is also a regular concern on Feral Worlds, especially amongst warrior-cults prone to infiltration by agents of Khorne, the Blood God; constant vigilance and regular belief-modification enacted by agents of the Ecclesiarchy are a necessity.