OK: props to the folks over at Total War Center, [link]
, from whom I got the majority of my info.
The Earth as the year 30,000 AD approaches has been through quite a lot, as has humanity. The First and Second False Space Ages and the first True Space Age. The Planetary Colonization Era. The Asteroid Wars and the Gene Wars. The Universal Republic era. The Swarm of Worlds and the Interplanetary Wars. The period of VR Stagnation and its bloody and still mysterious end. The First Interstellar Age with its slower-than-light generation ships. The Solar Empire period. The First Great Death. The Diaspora and Fragmentation. The discovery of Hyperspace. The Rejoining of Branches. The Opening of the Closed Worlds. Etc, etc, with millennia to go before the Federation of Man and the technological peak of human civilization.
The Earth has seen several world governments come and go, and has suffered horrendous damage several times, by asteroid bombardment, antimatter weapons, and biological agents: fortunately, humanity’s ability to survive has increased with its ability to destroy, and there have always been survivors to rebuild, with a nadir of a few tens of millions in bunkers near the core-mantle interface: the population has at other times numbered in trillions, requiring enormous cooling surfaces extending far above the atmosphere to radiate away the excess heat. During the most devastating of attacks, a large portion of the Oceans boiled into space, and the ecosystem was so damaged as to require its rebuilding essentially from scratch using genetic banks (there is still some disagreement as to whether the Unicorn was a pre-existent species or not.) The shape of the continents has further been changed by various efforts in planetary engineering to create more living space, while some annoying, ice-age causing variations and wobbles in planetary orbit and precession have been eliminated.
The most extended Time of Troubles has been the last four thousand years, during which humanity was first nearly exterminated by its own robotic creations, then saw its galactic empire broken up by warp storms making FTL exceedingly unsafe, was attacked on almost every major world by hordes of demons using psychic channelers as gates, was consumed by civil wars (often provoked by said demons) and plagues of madness, all deriving ultimately from the realm of Chaos. Earth survived, but was devastated to the point where functional planetary government ceased to exist and the majority of the population again perished (several wars with Mars didn’t particularly help either). In the end what civilization remained was reduced to brutal and disciplined little dictatorships scattered about the planet in fortresses and underground refuges, from which new states slowly expanded into the radioactive, monster, demon and mutant-plagued wilderness. Much technology was lost, in part due to the number of survivors being insufficient to maintain a truly high tech society.
In the current time, the world has been largely divided up between a few giant powers, smaller states mostly having been wiped out or absorbed. Republicanism is largely a forgotten philosophy, states usually being monarchies or autocracies or theocracies of various sorts: the notion that the common man in the tunnel should have a say in how things are run is considered childish and unrealistic. Societies tend to be highly conservative, paranoid and xenophobic, the consequence of millennia of terrible wars in the past. People are generally not very religious but highly superstitious – which in a world where actual demons and wizards exist, is perhaps not an entirely unreasonable point of view. Science as a vocation or an enthusiasm rather than punch-clock operation is looked upon with a great deal of suspicion, and several governments actively persecute those accused of practicing “scientism”: the verdict of history is taken to be that there are some things in which Man Was Not Meant to Meddle, and that “scientists” are people that if they see a big button labeled “DOOMSDAY MACHINE ACTIVATOR: DO NOT PUSH”, they’ll almost certainly push it to see what happens. Engineers, people who know how to keep the machines working and perhaps improve them a bit, are highly valued, but research for the sake of research is considered very sketchy.
Space travel is largely unknown: there generally doesn’t seem to be anywhere to go. Luna is unified, heavily armed, and deeply agoraphobic. Mars is run by a theocratic technocracy, and is downright hostile. Venus got blown to bits at some point, and radio signals from the outer planets do not seem convincingly human. Warp storms make FTL travel impractically dangerous. The general attitude is exemplified by the fact the bigger nations maintain massive dug in laser cannon to shoot down any visitors from space.
Technology is an odd mix of surviving elements: quite a few lines of technological development have just petered out or been discarded as impractical. Others have been forgotten in the eras of chaos, and without any real R&D beyond “steal other people’s tech secrets”, have not been rediscovered. Artificial intelligence of any sort is verboten, due to memories of the war with the robots or “iron men” (Cleverbot would be ruthlessly exterminated). While fusion power and near-indestructible building materials and all sorts of genetically engineered plants and animals exist, the technology for antigravity propulsion has been lost, and with it pretty much all forms of air travel, ancient-type jet or propeller driven craft being considered too fragile or too poor in carrying capacity to be useful for military or mass transportation purposes: only a few nations field flying machines, and in most airplanes are at best toys for the rich. Colossal armored trains capable of carrying hundreds of thousands of people are the normal intercity transport. In combat, power armor is king: the loss of disintegrator tech means that good ol’ hand-to-hand fighting has come back into its own, since regular gunpowder and explosives aren’t able to crack a good suit of armor. Heavy artillery is needed, and given the high mobility of troops in power armor, these in turn need more troops in power armor to defend them. Some nations have the capacity to build powerful hand lasers, but even they take a while to cut through the kind of super-strong materials power armor is made of, and it’s hard to keep a laser focused when the target is advancing towards you in 50-foot bounds and wielding a 10-foot vibrating monomolecular blade capable of slicing an OTL tank into pieces like a sushi chef chopping veggies.
Admittedly most nations do not have the resources or industrial capacity to fully equip their hordes of troops with cutting edge power armor: most troops in the world have third-rate armor just capable of moving itself easily, and are equipped with weapons frequently more dangerous to themselves than better-armored opponents. But then in this world the term “cannon fodder” is used un-ironically, and if 50 low-level troops must be expended to get rid of one foreign elite, then so be it.
War vehicles tend to the massive and lumbering, motile forts bristling with artillery and guarded by armored troops like actual forts. High explosives, super-hot incendiaries to cook people inside their armor, and even low-yield nuclear weapons are all part of the normal battlefield experience: and then of course there are the ugly surprises. Most nations have stocks of ancient, no longer duplicable weapons, and often will bring some surprise doomsday weapon into play at a strategic moment. A few weapons have been discarded: the effects of long-term radiation induction weapons are so counterproductive, leaving vast areas unusable for many millennia, most notably in the early years of Brasilian expansion and the great war between Ursh and Afrique, that even the maddest of dictators has taken them off the table. But hive-city cracking atomic cannon, radiative “death zones”, bioengineered mountain-sized monsters, earthquake generators, etc., are all acceptable tools if the objectives are important enough. And then there is “magic.”
Magic is what psychic channelers, “Psychers”, who can access the Primal Chaos which underlies hyperspace can do. The very fabric of reality can be warped and distorted, and grotesque horrors result. It is horribly dangerous stuff, since its use attracts the monstrous inhabitants of Chaos, demons more terrible than any medieval nightmare, and an incautious Psycher can easily end up providing a channel to our world for such, in some cases just ending up mentally taking over the Psycher (and often anyone else in the neighborhood), more rarely physically manifesting themselves. And if enough power is used, there are worse things than demons in the depths of Chaos: there are beings which for a lack of a better word are referred to as Gods by those in the know, creatures who feed off the pain and lust and madness and greed and disorder of every living thing in the galaxy. And they might notice…
However, the chances of magic being useful in some desperate situation (especially if the other guy is using it) seem high enough that pretty much every nation dabbles in it (being a psychic channeler is supposedly a death sentence in most countries, but who is to say what becomes of people the state just “vanishes?”): a few, such as Ursh and the Nordafrik Conclaves, dabble on a rather larger scale.
Populations have bounced back briskly: society is generally sexist, large families remain the norm, and birth control is discouraged (a steady supply of fresh combat-age males is usually pretty much demanded by the state). Populations are in fact far higher than OTL 2012: a combination of synthetic food production and genetically engineered “super-plants” vastly more efficient in converting sunlight into food than the crappy chlorophyll-cycle systems of today means that over 50 times as many people as today can be successfully (if rather boringly) fed: global population approaches 400 billion. Most of these multitudes are crowded into giant cities often referred to as “hives”: not only does this maximize land available for food production, but serves as a response to the insecurity that has been the plague of so much of the last few millennia – each hive city is essentially a gigantic fortress, a massively armored structure in some cases over two miles high, with outer walls often hundreds of feet thick, divided into separate outer and inner layers by massive internal security gates: the ruling classes generally live deep within the structures, with many layers of armor, troops, weapons, etc. between them and any attacker.
Although the larger powers have been mostly at peace for some centuries, a certain low-level skirmishing and testing of strengths goes on almost all the time, and the desolate radioactive borderlands and deserts too harsh for even the super-plants to grow are inhabited by marginal peoples, some with the technology to produce synthetic foods, others surviving by raiding the agricultural lands of the established states. Some are techno-barbarians, living off of a highly stripped down but endlessly repairable or self-regenerating technology package: others are sub-races, branches of humanity mutated by radiation or bioweapons, shunned like lepers by “base type” humans: still others are aliens stranded on Earth by the warp storms, forced to flee into the wilderness when desperate humans began to ask why are we sharing food and water with them? None of these really count as a serious threat to the major human powers, loose talk about “mutant hordes” nowithstanding, but they do make convenient bogeymen. A more serious threat is the occasional wilderness communities of psychics and chaos channelers: they often self-destruct in an eruption of demons, but sometimes they gain some stability under a powerful leader, and have on occasion destroyed or taken control of hive cities. Even dead Psychers still can cause trouble, if the Things that they have carelessly summoned decide to hang around after horribly killing them. There are also a variety of nasty mutant animals, which in spite of frequent massacre, still continued to survive through Ludicrously Fast Breeding
There are at least five different species of intelligent aliens surviving in desolate parts of the world: the reptilian species of the Brasealean southern deserts have made themselves experts in concealment, for they are hunted by elite troops who decorate themselves with their skins. The most successful are the octopus-like creatures who monopolize the deep sea environment: they will come close to their goal of developing technologies to hold the surface world hostage, but before that occurs the God-Emperor will exterminate them as a small side job to his main task of reunifying mankind.
The landscape is usually covered with a thick tangle of the dark, almost black food plants where it’s not radioactive rubble, frozen wastes or baking-hot desert, the vegetation extending in floating mats far out onto the ocean. Huge harvesting machines grind along in the distance. Here and there, the straight line of a train-road bisects the landscape, and something like a row of ocean liners shoots along it at a few hundred miles an hour. On the horizon, visible a hundred miles away or more, one may see the mountainous form of a hive city. There is wilderness here and there, strange tangles of mutated vegetation, some terrestrial, some alien in origin, usually located in disputed border areas or in the radioactive fringe lands of a dead zone. In a few places, wilderness has been deliberately set apart by kings and dictators to provide a little touch of real nature for elites to enjoy. Aside from the hive cities, the landscape includes huge mining complexes extending down tens of miles into the planetary interior (the upper crustal layers were mined out long ago), smaller-than-city-hives-but-still vast defensive fortresses bristling with artillery, and agricultural tending stations (usually including a posting of troops. Far worse pests than aphids may be lurking in the vegetation).
The Dead Zones were exposed to particularly lethal forms of atomic energy which has rendered them nearly permanently radioactive, remaining uninhabitable even after millennia. Areas with merely normal fallout are hardly even worth putting on maps. Only a few rare and exotic forms of life survive in these areas.
People tend, after so many millennia, to be racially mixed. Of course, given human phenotype manifestations, any population will show a variety of types, dark skinned, light, dark, blonde, etc. What was once East Asia, due to its massive demographics, still tends to look a bit Asian, and what was formerly Africa is a bit dark, but the rest of the world is a hodge-podge. (Generally the spectrum of human shades is hued a couple shades lighter than would be the case if most people didn’t spend their lives in Caves of Steel or in gas-tight suits of combat armor). Although various efforts over the millennia to seriously upgrade humanity through genetic engineering, etc. have generally ended in tears, many small patches have added up over time: people are generally healthier, taller, considerably longer lived and far more resistant to cancer and heart disease than people of our day. Not having us to compare their selves with, Earth’s crowded, disciplined billions derive no pleasure from this fact.
Neither the racial mixing nor the fact that pretty much all human languages are decayed offshoots of a planetary common speech developed in the 24th millennium has prevented the development of new nationalisms. With no clear national history after centuries of chaos and warfare, many nations have taken identities from long-ago nations and states in areas roughly corresponding to their present locations.
Merika, perhaps the world’s richest and most developed state, and the third most populous (second if its vassals to the north are counted), claims a continuity going back to the ancient Usah empire. It is true that a regional identity of sorts has continued throughout many millennia and multiple changes of world government, and during periods of disunity some sort of North American state has reemerged more than once, but by the late 29th millennium the USA exists as little more than a myth of good government, prosperity and freedom (freedom being imperfectly understood). Still, it is a powerful legend, and the colossal capital of New New Yawk (which has more people than the entire 2012 USA) was built where what was assumed to be the “statue of liberty” was uncovered during a mining operation. (The statue actually dates to the 21st millennium, is made of starship hull-metal, and was built closer to old Boston than old New York, but it did have a kinda sorta liberty theme, so there’s that). The Merikan government is essentially a military dictatorship, but the swarming billions are mostly left to live their lives without much interference from the central government (not that there aren’t plenty of petty local tyrants in the hive cities, but their power too is limited). Of course, much of the prosperity, and the fact that Ursh hasn’t dared attack in half a millennia, may have a lot to do with the fact that the most powerful Psycher in all of human history, the man who will be the God-Emperor of Mankind, is currently hiding out as a humble member of the government and manipulating things behind the scenes.
Calbi (known of old as Great Alba) was an fierce enemy of Merika in ancient times, but is now a tightly controlled vassal, dependent for certain raw materials and foodstuffs (even the super-plants can only do so much with the climate, and Calbi synthetic food technology is not of the best), and providing extra warm bodies for Merika’s armies. It has an identity largely divorced from that of old Canada, which left only a few legends (such as the tale of the ever-filled pot of poutine), and only vaguely tied to a half-mythic English identity among certain subgroups. Most of the population is concentrated in a small number of particularly huge hive cities (the better for the Merikans to police them).
To the south lies another old enemy, Hy Braseal, which has a national identity compounded out of bits and pieces and random scraps, but oddly enough still know how to throw a hell of a party. Currently the government has some democratic elements, with the national parliament having some real power. As international tensions rise with the approach of the Age of Unification, this will change for the worse. Brasealians are noted as breeders of giant gene-engineered monsters and as artistic architects, within the limitations of “massive fortification” architecture. It is bordered by one of the most badly damaged parts of the planet, which separates it from the somewhat isolated Antarctic Kingdoms.
The Antarcticans live mostly underground, and grow or synthesize their food down below. They have dug out an incredible system of tunnels over the millennia, for obscure reasons far more than are needed: there are millions of miles of tunnel down there, the majority no longer used. Although loosely unified under a High King, the bonds between the Kingdoms are weak, and they fight frequent ritualized battles atop the ice. Their culture has few if any historical antecedents.
The eight states of more-or-less Europe are of comparatively little importance, with a combined population a little over a quarter of that of Merika. There is also quite a bit of reaching when attempting to create new identities: the “new Roman” identity that the Europians are using as a template is of an inaccuracy that would embarrass the SyFy channel, while the Duscht Jemanic have so vague a grasp of German history that they hold the belief Hitler was some sort of cool guy, and use the Swastika as one of their national symbols. (There are people in the 29th millennium, followers of a minor cult identity,  that are frankly unaware that a chap called Hitler once killed a bunch of followers of an ancient faith theirs descends from). The Skand have a strange religion and odder customs, and generally gruesomely sacrifice people they capture in wars: there are some who say they are genetically distinct from most of humanity, and not in a good way. Gredbritton, which has been ruled by the same line of kings for half a millennium, is noted for its multitude of small, scattered cities (aside from the capital itself, none exceed a mere five million: practically villages) and a mysterious secret cult of assassins that protects it from foreign enemies, which holds a trove of ancient super-tech including the only operating anti-gravity war flyers on the planet, reporting to a leader known only as “M.” 
The most important local force is the Quintuple Alliance, a grouping of countries banded together to deter further Ursh expansion after the destruction of Afrique. Aside from four “European” nations, it includes the powerful Achaemenid Empire (their historians confused a dynasty name for a national one: the geographical location of “Persia”, and its relationship with “Iran”, remain hotly debated). Other members include the small-scale industrial powerhouse of Uralia, whose principal tie to the ancient Russians is a formidable capacity for booze, and the remarkably innovative little nation whose people call themselves the Terrawatt Clan – a nation where a certain self-important immortal has fingers in many pies.
The peculiar oligarchic, mystical and highly refined culture of the North Afrik Conclaves bewitches and occasionally frightens outsiders, who hear many rumors of the strange powers and forces and powerful ancient machineries commanded by this nation. These rumors however inflame greed and ambition rather than provoke caution in Ursh, where the national sentiment is that the inevitable expansion of Ursh to global dominance has too long been delayed by a sickly and cowardly peace: if the Conclaves have unknown super-tech, then it will be added to the arsenal of Ursh.
Ursh is the largest and most populous nation on earth, incorporating lands that used to be India as well as much of interior China and north Asia. It is also a harsh totalitarianism somewhat mitigated, as the expression goes, by assassination. It freely dabbled in the dangerous powers of Chaos – and indeed it is hard to say to what extent its ruling classes have been corrupted by these forces. Obedience and discipline is all, from the highest general in a palace-mountain to the lowest pipe-scrub boy in the foulest sumps of the most hellish of hive cities. Its identity is drawn from a variety of earlier totalitarianisms, from the 20th century to the 16th millennium.
Perhaps the most terrible war fought on Earth in the last three millennia was that between Ursh and the Afrique League, at the time the largest, most populous nation on earth, if a bit backwards and politically rickety. It ended in the greatest unleashing of doomsday weapons since the destruction of the lost Polar Empire, and shattered the League for all time: its former lands are now divided into the realms of petty dictators, Ursh puppet states (kept weak and divided), and a couple civilized (well, by this world’s standards) states separated by vast areas of chaos and radiation and jungles inhabited by unholy monsters.
The Pan Pacific Bloc, which looks back to Chinese imperial models,  (in spite of the fact that the current ruling family’s name clearly proclaims a European origin) is a harsh dictatorship, but lacks the whiff of Chaos that makes Ursh so worrying. Its people are second in wealth only to the Merikans, and its leaders are proud and haughty. Having fought several bloody and inconclusive border wars with Ursh (in the last of which they were forced to irradiate a vast swathe of their own country’s borderlands to block and Ursh advance) they have occasionally attempted to create a grand anti-Ursh alliance, but the Merikans (with which they have in the past clashed in Pacific waters) aren’t buying.
The region that became Yndonesia, during the chaotic centuries after the Warp Storms, began converting from a purely secular high-tech society to followers of a peculiar offspring of the ancient Christian faith. It eventually evolved into a militant theocracy: not strong enough to expand further in opposition to powerful neighbors, it has turned inwards, seeking to create a “pure” society through mental programming and a bit of eugenics. Even more hostile to a “scientific” mindset than is normal on this world, the Yndonesian Bloc has begun to slip behind the rest of the world in technology, although given the low level of contact with “infidels”, nobody has noticed yet. Like Antarctica and to some extent the Conclaves, its culture is uniquely its own and draws little from ancient models.
Hundreds of miles down, a few deep-mantle protective vaults are still inhabited, by cranky little civilizations which, knowing the surface world has gone to hell, are by gum going to stay where it is safe. Some will survive even after the God-Emperor has made the entire surface of the planet into one galaxy-dominating city, because he finds them amusing.
 Barely half a billion of them world-wide!
 M as in Bond's boss? M as in Mycroft or Moriarty? M as in Merlin? That...is a secret.
 From the POV of the 29th millennia, the period during which Japan was a serious challenger to China is an almost invisible historical blip.