Earth glitters seen from space: from the tiny motes of interplanetary and interstellar craft constantly entering and leaving its atmosphere, from the many space stations in orbit, from the brilliant lights of cities on its dark side. It is a world of super-science, where progress speeds along at a dazzling pace as new technology from other worlds and solar systems arrives to shake things up on an alarmingly frequent pace.
Earth's history diverges from ours in 1936, when earth began to be bombarded with mysterious fireballs from space, a "softening up" terror weapon from Mongo: over the next three years tens of millions of 5-meter balls of immaterial flame would fall from the skies, starting fires in cities and forest and grassland that would kill millions, and cause billions in damages. And then the planet Mongo itself, first misidentified as a comet, would pass within a few million miles of Earth, only veering off in time (its guidance controls locked and destroyed by Gordon and his friends) to prevent utter devastation, although the earth was still hit by earthquakes and tidal waves and storms from Mongo's proximity. Mongo would return again and pass even closer in 1948, during the final struggle against Ming.
Hitler being Hitler, he didn't let a little something like the planet almost being wrecked and a second massive economic dip stop him from trying to conquer Europe, but in spite of some gifts of advanced technology from Mongo, he failed as thoroughly as OTL. The return to Earth of Flash, bringing advanced technology, and regular contact with the planet Mongo essentially short-circuited the Cold War (for one thing, with an American being good buddies with the ruler of Mongo, the Soviets were much politer).
Earth gained greater unity in the 1960s and 1970s, as a result of the long war fought by Earth, Mongo and their allies against the savage, warlike Scorpii, a race of aggressive, insectoid beings, not finally ending in victory until the early 1980s. The World Federation is still looser than most one-planet thinkers would like, but the Planetary Council (currently meeting at the World Tower on sunny Cyprus) is an actual government with actual powers: in conjunction with the all-Planet fleet (the World Space Patrol) of ships interplanetary and interstellar, it handles relations with other worlds and civilizations, whether for war or for peace, and coordinates economic development and negotiates relations between the member states. The World Science Council is a whole other kettle of fish.
The Soviet Union is still around, super-science having to some extent made up for the problems of central planning, and has evolved into a relatively democratic federation, while China has reestablished Imperial rule after the Spring Revolution, a rare case of Earth imitating Mongolese political traditions. Broadcast power and nuclear energy (a lot cleaner than that of our dimension) have made petrol fairly unimportant except as a chemical feedstock, and Saudi Arabia remains rather unimportant in international affairs: the Palestinian problem has been solved by giving them their own homeland on the Venusian highlands (with rather less monsters than the lowlands and unmolested by the warlike but moisture-loving sponge-men of Venus) . Europe is unified, and Africa is being energetically developed with a lot of foreign input and development in a Let's Not Look Bad in Front of The Neighbors reaction.
As Earth colonizes Venus, the asteroids, the moons of Jupiter, and various bodies in several dozen other solar systems, some grumble that Earth is being colonized in turn by aliens: an increasing number of inhabitants of Mongo are moving to a planet where there are less hereditary tyrants, well-meaning or not, and where the wimpy have less to worry about in terms of swaggering bravos with electrified swords and jeweled codpieces, and courtship is less likely to involve duels to the death. Martians, too, are moving in, as are skeleton-men from Ganymede, Gelatinous Blobs from far Antares, robo-men from Skorpios, etc. In a galaxy full of ancient Science Dictatorships, Cosmic Empires, Eternal God-Kings, Robot Overlords, etc., the easy-going nature and the merely centuries old bureaucracies of many Earth governments are practically pastoral anarchy by comparison. There is increasing grumbling that the World Federation needs to do something to stop the inflow of Space-Backs.
Technology has moved forward alarmingly fast over the last half-century, as a result of the introduction of Mongolese technology and also new sciences picked up from other worlds as Earth has expanded into space, most notably in the war with the Skorpii. There are waay too many kinds of rays: death rays, disintegrator rays, freeze rays, paralysis rays, combustion rays, mind control rays, invisibility rays. Thought-projectors allow for communication at planetary distances with no interference problems, antigravity beams allows the suspension of buildings or cities in the sky. (In those countries where the insurance will cover it, anyway).
Nuclear rockets travel now to the other planets in the solar system in a matter of days, and the space-drive has brought the stars to within weeks or months. Force fields protect ships and hold in the air around asteroid settlements. Robots exist but remain rare: the population was somewhat soured on them when the Scorpii subverted Earth's robot forces with the aid of the Machine-God of planet 1100110000100111000010110011110110001.
Privacy is a problem: a variety of energy screens are necessary to first keep the government or some mad scientist from peering into your house with a space-o-graph, and then keep psychics from poking around in your head: with the aid of psi-tech from Mongo and the mysterious Mind Masters of Planet Z, human psychic talents have been scientifically identified and harnessed at last, a development that induces a great deal of paranoia in many. Still, the government won't call off the psi-corps program anytime soon: an international network of trained psychics is one of the Earth's few potential advantages over various alien tyrannies in the depth of space (alien dictatorships by necessity tend to keep their psychics on a very short leash or simply eliminate them entirely).
Stylistically, the cities of Earth are rather lacking in ornament, great glittering towers of super-glass and alien alloys, regular, geometric, prismatic. The costume of Earth people is also orderly, suit and tie or space armor or jumpsuit with lots of pockets. Even the new cities of Africa seem carefully cleaned for inspection. It is an expression of Earth's seriousness, sophistication and high civilization, or what it hopes is such: the dreadful backwardness by galactic standards of Earth only sixty years ago gives rise to a sense of inferiority that is always being combated. Unlike OTLs Japan (for in a way, this has been Earth's Meiji era), imitation is not the agenda: there are after all so many alien cultures that there is no single standard of galactic modernity. Instead, there is competition of sorts: competition with Earth's sometimes ally, sometimes opponent, the planet Mongo. A world which combines super-science and barbarism, ray-guns and sword-fights, floating cities and gladiatorial contests, robot armies and ridiculously elaborate costumes with very short pants. Look, says the Earthling to the rest of the galaxy, we're just getting the hang of modern science but aren't we a more civilized, more sophisticated people than Them?
Between the orbits of Jupiter and Saturn circles Mongo. It is a world larger than Earth, with several times its surface area: given its orbit and size one might guess it to be another gas giant: to the telescope it shows a luminous, orange face, perhaps indicative of a deep atmosphere rich in complex molecules. However, this is quite illusory.
In fact, Mongo is the blue of seas and the green of jungle and the white of clouds and the red and yellow of deserts: it is an earthlike world, and the orange haze is in fact artificial: an aura of radiant energy, that brings warmth and life to its surface in spite of its distance from the sun. And its surface gravity is actually lower than Earth's. For Mongo is not a natural planet: it is a made thing, its interior largely hollow, its gravity artificial, and its "sunlight" generated by vast machines at the poles. Indeed, it has only been in its current orbit since the 1950s. Before that Mongo was a travelling world, a cosmic marauder, driven through space at times faster than light by unimaginable forces, their "wake" able to rip apart the surfaces of other worlds at distances of hundreds of thousands of miles. At times Mongo has leapt almost instantly vast distances across the galaxy by artificially induced wormholes, using the energies of deliberately exploded suns.
It travelled to conquer and terrorize, to plunder and enslave. Mongo was a name for terror, for it was the world-ship of Ming the Merciless, the most fearsome villain in all the known galaxy, who ruled Mongo and controlled its machineries for centuries. Perhaps millennia: nobody on Mongo knows for how long it has travelled, since most of its inhabitants were not originally people of Mongo, and the oldest inhabitants no longer possess records of the beginning. It is unknown as to whether Mongo was actually created by Ming (as he claims) or simply stolen by him at some point (which nobody dared suggest in public).
Besides vast empty wastelands and great, dark, tideless seas, Mongo is a patchwork of kingdoms and states, differing greatly in their geography and inhabitants and even flora and fauna: for few, if any, of the inhabitants of Mongo are natives. In fact, they are all races whose worlds have been conquered and wrecked by Ming: after subjugating their worlds, by a fantastic scientific process the more favorable parts of the planetary surface and crust have been transferred to the surface of Mongo, along with their inhabitants, leaving their original planets in a state of ruin. Mongo is a pirate world that adorns itself in the skins of its conquered worlds.
(It is an open question as to when Mongo will get "full up": there are still vast areas of uninhabited wasteland. And there are ancient records that seem to indicate, fantastic as it may seem, that Mongo has grown larger since early times: this is one of the Deep Mysteries of Mongo).
Mongo is rich in weird life forms, including what to visitors seem to be an excessive number of monsters: this is no accident, since collecting and breeding monsters was another hobby of Ming.
The inhabitants of Mongo include (and this is not an exhaustive list) the fearsome blue dragon-men and their black jungle cities: the fierce lion-men, a people scattered and few, for they could never learn to bow to Ming: the cold-blooded, technologically advanced humanoids of Frigia,  who change to summer clothes when temperatures rise above the freezing point: the mole-men, in their endless tunnel cities deep beneath Mongo, occasionally warring with the also cave-dwelling lizard-men: the stolid tusk-men, farmers and laborers: the fire-men, who live inside volcanoes and wear asbestos armor not to protect themselves from heat, but as insulation from cold: the amphibious, green and scaly shark-men of the oceans and their underwater cities: the anarchic red monkey-men: the mysterious blue-skinned inhabitants of the kingdom of Syk, whose science is indistinguishable from sorcery: the hot-blooded humanoid inhabitants of the jungle land of Tropica: the savage fur-men of the great mountains: the hawk-men, whose land has been rendered waste, and live a nomadic existence in their flying cities: the dwarves of the Magnetic mountain: the strange, half-energy "power men" of Mongo, and their crystalline cities: and the forest-dwellers of Arboria, the greatest hunters and trackers of Mongo (or so they claim: the Lion-men dispute this).
Mongo is currently ruled (more or less) by King Taris, son of Barin of Arboria, who became ruler of Mongo after the overthrow of Ming in 1948 and retired due to increasing age in 1996. (He still rules as king in Arboria, but the throne of Arboria will pass to another of his sons upon his death, so the combined rule of Arboria and Mongo as a whole will end with him: this was to satisfy some of the other kingdoms of Mongo, who felt Barin favored his own kingdom above the rest). Taris is descended from Ming by way of his mother, princess Aura, which reconciles Ming loyalists (and they exist: Ming was worshipped as a god by many) to his rule.
Rule, again, "such as it is." Ming himself had ruled with a relatively light hand over the many kingdoms for lifetimes before his overthrow it amused him to set kingdoms against eachother, or to wait for conspiracy or rebellion to arise and then crush it with brutal force and the various kingdoms very much prefer King Log. Taris only rules firmly over Ming's "Central Realms", an extremely rich and productive kingdom of some ten billion inhabitants, made up of many races and sub-races besides from the yellow-skinned (as in various shades from orange to pale lavender, rather than terrestrial Asian racist stereotype "yellow") majority, and even there democratic ideas from Earth are penetrating. Even if he wanted to make himself into a tyrant over the rest of Mongo, he lacks Ming's vast network of spies and brainwashed agents, his armies of killer robots and hideous mutants, and much of his sinister science: the best he can really do is preserve the peace among the various kingdoms and see that no true tyrants appear (a little dictatorship is normal enough on Mongo to be acceptable, as long as it doesn't get too baroquely awful. Indeed, Earth ideas fascism, communism, democracy are currently more of a disruptive force than is good old Mongolese absolute monarchy.)
Of course, Ming would not have been overthrown in the first place if a home-made rocket piloted by one Dr. Hans Zarkoff (half-Russian-half-German refugee from the Soviet Union, and World's Greatest Scientific Genius), and carrying the not-entirely-willing crew of Dale Arden (tough-as-nails Girl Reporter, masterful bull-shitter, and surprisingly Machiavellian strategist) and Flash Gordon (all-American, Olympic Polo and fencing medalist, and all-around Good Guy) hadn't arrived on Mongo late in 1936. After twelve years of fantastic adventure (with only a brief visit back to Earth to stop the Nazis from destroying the US with a super-weapon Ming had apparently given them just for shits and giggles), Flash and his companions brought about an alliance stronger than any in the history of Mongo, with the help of Zarkoff cracked the secrets of many of Ming's superweapons, and at last overthrew Ming's rule. (Admittedly, over the next few decades he would show up again and threat Earth and Mongo not to mention Mars no less than three times, twice thwarting seemingly Certain Death. However, he hasn't been seen since the 1970s and it is hoped he is gone for good).
The man who made Ming's overthrow possible is still alive at a century of age, thanks to his and Dale Arden's exposure to the mysterious rays of the Life-Crystal on their adventure on Planet of Red Night: although his hair is now white and his face marked by many lines of care and laughter, he is still tall and strong, bronzed with the light of strange suns (and with shiny, white, and entirely artificial teeth). Earth's greatest hero is largely retired, although still honorary head of the World Space Patrol (and head of the joint armed forces of Mongo, Prince of Tropica, honorary high priest of the God X'heela on the planet Adoth-Plune, head of the international Polo association, etc.) His and Arden's children and grandchildren are a remarkable bunch themselves, space explorers, scientists, military heroes, and the current President of the World Federation. The black sheep of the family, their grandson Thune, became a space adventurer and eventually dictator of the planet Oool.
Flash keeps himself busy running his 6000 acre horse ranch on Venus (the next high plateau over from the one with the Palestinians on it), but can't forget how much he misses Dale. Dale and Flash, although still married, have been separated for almost a decade: she finally got tired of either being stuck at home while he risked Certain Doom or coming along as his sidekick, and being almost ravaged/experimented on/thrown into a pit of man-eating space oysters for the umpteenth time. She has currently returned to her reporting roots, and her talk/news show Dale's Den is among the most popular Tri-V shows in the solar system.
In the meantime, an ancient and nowadays more metal than flesh Dr. Zarkoff, the Smartest Man on Earth, with more patents than Edison and a large laundry basket full of Nobel prizes, has largely vanished from the public view, working (supposedly) on some great new projects for the Betterment of Mankind in his Adamant Tower at the north pole of Pluto. In fact, he is pursuing the mystery of his own self: investigation of the roots of his own scientific genius, beyond that of any other terrestrial, long ago led him to discover that his genetic heritage was not wholly human. He suspects the man who left him his surname was not his true father: if he can complete his chrono-scanner, his past and the secrets of his origin may at last be revealed.
Mars red, dry, full of canals, with its spindly purple trees, spindly white towers, and spindly red people, is an ancient and civilized world, and has returned to its Traditional Order after the overthrow of Ahz'urha, Ming's puppet ruler and catspaw. Those who opposed her have been cured of the Clay Plague (a Ming-created virus which turned its victims into slimy, grey-skinned creatures unable to stand the touch of sunlight) and her supporters among the Golden League (who had wished to return Mars to its ancient days of warrior glory) have been very thoroughly purged. The Crown of Mars has returned to its traditional elective role, but many Martians will declare that if Flash were to return, the Crown would be his for the asking. (Flash isn't falling for it. Martian court protocol has been evolving for millennia and makes the Imperial Ming court look rather more informal than a hippie commune. Besides, he's a true democrat).
Beyond the solar system, although there are many utterly alien intelligences, there are also many humanoids races to be found among the stars, some of them of terrestrial descent, as a result of the efforts of the mysterious Elder Ones (they did something quite different in Andromeda and the next couple galaxies over, but the locals don't know about that, so the non-humanoids grumble a lot about what the hell is so special about jointed bisymmetrical bipeds). Flash named the planet C'Taar (pop) lrg'l "Lemuria" not only to make it pronounceable, but because the pacifistic bird-people who inhabit it are actually genetically modified descendants of Earth-people saved from the flooding of an ancient continent in the Pacific.
After a long struggle, the Scorpii Empire did fall at last, and most of it was carved up by various old enemies and fair-weather vassals: a shrunken rump survives as a joint Earth-Mongo protectorate. The fall of the Scorpii sent ripples along the length of the galactic arm: whispers travel across thousands of light-years that there is a new player in the galactic game. But what is their relationship to the pirate planet Mongo? Is it true that Mongo has ceased to travel and pillage? Might the ultimate secrets of its existence be revealed at last? Spies and agents of various galactic powers prepare for the long voyage to the solar system and the mysterious planet "Earth."
And halfway across the galaxy, Ming looks on as the former co-Emperors of the Bullan Empire battle with daggers for his amusement. The Empire is now firmly under his control, with the elite subjugated through a liberal use of mind-control rays and his robot monsters to intimidate the rest. Soon the new war-fleets will go into mass production. Soon, a star will be destroyed to create a bridge across the galaxy. Soon, Mongo will be his again.
He has grown tired of the game. He will not admit that it was because he was losing too often. He has always won in the end, and he will do so again, for is it not his destiny? His purpose, to conquer the entire universe? He is Ming, and all that exists will bow down before him: for is he not the center, the pivot, the reason for the universe? He is Ming. The Merciless. The Supreme. The Eternal.
 The Palestinians, ungrateful folks that they are, complain a lot about the "not being asked for their opinion" thing.
 Most of the names are those given to them by Flash Gordon in his accounts of his adventures: the actual names usually do not easily trip off the tongue, either in the Common Speech of Mongo or in the local languages: Frigians, for instance, are all about the glottal stop.