In 1632 the Holy Roman Empire is this for a short time before being officially dissolved about two hundred years ahead of schedule.
In the world of The Anglo/American – Nazi War, the Soviet Union loses to Nazi Germany. The vicious treaty imposed upon Soviet Russia robs them of an army, as well all its territory west of the Urals. After the new capital of Krasnoyarsk is nerve-gassed by Nazi bombers in the final months of the Second World War – killing most of the government – the country collapses into civil war. By the early 1960s, European Russia, East and West Ukraine, Belarus, the Baltic States and the Central Asian "-stans" have broken away permanently, while the Russian Far East has joined the United States as West Alaska. All that remains of the USSR is western and central Siberia.
Belgariad: Tolnedra (although most of the countries around it were never really under its political influence, they still act as if they controlled the whole continent once upon a time). They are a greater force for law and order in large portions of Arendia than the Arendians are, and the backstory details how they basically forced the other countries to create Sendaria at one point.
Many governments and their militaries in the Black Tide RisingZombie Apocalypse series, after the Hate Plague hits them, are almost totally destroyed, the surviving rulers controlling only a relatively small part of their original territory.
The nation that serves as the primary setting of the Book of the Ancestor trilogy is simply called the Empire as is implied to have once lived up to the name, but by the time of the novels has diminished to a fairly small kingdom besieged by encroaching enemies on all sides. The most powerful of those enemies, the warlike, expansionistic kingdom of Scithrowl, plays The Empire trope much straighter.
The Commonwealth in Book of the New Sun claims to be the successor state to the monarch's interplanetary empire, but in actual fact they only control part of one continent on Earth. Still, the interplanetary civilization recognizes the Autarchs of the Commonwealth as the legitimate spokesmen for Earth, which drives the entire plot ofThe Urth of the New Sun. Bonus points because the Commonwealth is an Expy of the Byzantine Empire in South America.
Several in the Chaos Timeline, most notably the remaining British royal family. They flee to New Albion (New Zealand) after Britain turns republican and eventually socialist. A civil war over throne succession issues eventually rocks the country in the 1960s and effectively splits it in two, the South Island standing behind the resident Cloud Cuckoo Lander and the North Island standing behind a certain Elizabeth. Talk about the British royal family being the Butt-Monkey of this timeline.
By Tamora Pierce, the Pebbled Sea states of Circle of Magic arose from the old Kurchal Empire, which gave them a common language and a calendar. It may also have been a bit Roman, as one character references its coliseum fights.
Daughter of the Sun: Xytae once ruled the entire continent and many lands beyond. Now it's only a shadow of its former height. While still commanding large territories, most of the continent is now made up of independent countries besides Xytae.
Subverted in Decades of Darkness. The Restored Empire, a loose union of former British colonies led by Australia after the fall of Britain itself, appears to advertise its empire-in-exile status in the title, but is actually the free-est, most vibrant, and nicest place in the southern hemisphere and possibly the world as of the timeline's end. At least for English-speaking people.
Ankh-Morpork is a rare example of a Vestigial Empire where main characters not only come from the corrupt and decadent city, but often spend the entire book there. Also notable in that while the actual empire is long gone, and the Patrician expresses distaste with recreating the idea ("We are not having another Ankh-Morpork empire; we've only just got over the last one"), the Pax Morporkia is still in effect in many places due to Ankh-Morpork's economic and cultural dominance, only now instead of 'Do not fight, or we will kill you' it is 'Do not fight, or we will call in your mortgages.' In this case, the closest historical parallel would probably be London.
Another example from Discworld would be Djelibeybi, Pratchett's analogue to Ancient Egypt in Pyramids. They only control a tiny stretch of river by the events of the book, but it's stated that they used to control most of the continent before they sold it all to pay for pyramids. They still serve a vital role, since it means the two local powerhouse nations don't actually share a border and have an excuse not to go to war.
Subverted with the Fjordell Empire in Elantris. On a map, Fjorden appears to be only a shadow of its once continent-spanning might, but it's far from in decline. Rather, its leaders recognized that attempting to militarily reconquer their old lands would be unfeasible, and so made an alliance the Shu-Dereth religion. The "new" Fjordell Empire fused its own political hierarchy with the Derethi religious hierarchy, and as a result it's actually far more powerful than it was in its heyday through the Derethi religious sphere of influence. Anyone who is politically aware in this world knows that Fjorden is far from the Vestigial Empire it appears as at first glance.
The Elric Saga has the Melnibonean Empire of which Elric was its last emperor. Until Duke Aubec's uprising, the Melnibonean Empire controlled the world and even extended its reach to other dimensions. After Aubec and the rise of the Young Kingdoms, the Melnibonean Empire is reduced to Imrryhr the Dreaming City.
The Guantanamo Regime is all that is left of the United States. It controls Guantanamo Bay, after a popular uprising against the mad and tyrannical Edward Butler regime. It continues to exist because Butler was able to storm off with several nuclear ballistic missiles and most of America's gold reserves. Butler rules as eternal President, the people are under constant surveillance, children are indoctrinated to follow Butler's paranoid ideology, and the prisoners who were in Guantanamo Bay are treated as slaves.
The Soviet Union-in-exile consists of lunar colonies and space stations that preserve the Soviet Union and reject capitalist Russia.
The last remnant of the Qing Empire in the world of "The Last Emperor" rules Kowloon, where it becomes a Wretched Hive for criminal syndicates, deposed dictators, and espionage intrigue.
The South African Republic-in-exile largely consists of the South African Defence Force, which is made up of a 40 ship-strong flotilla, taking shelter in the Portuguese exclave of Cabinda. Although recognized by the United Nations, the SADF's diplomatic and monetary lifeline that was extended to them by the international community lasted as long as the anarchy in South Africa did. The SADF resorted to becoming a global private military contractor. The Apartheid system is still alive in the former SAR, as the non-white populace is too small to vote themselves into power and an open rebellion would be suicide. The SADF are secretly determined to reclaim their old homeland, by any means necessary; they use their vast funds from their "humanitarian" operations to destabilise the South African successor states. Furthermore, they have undeclared nuclear weapons obtained from the former People's Republic of China and are planning to use them to wipe out the successor states.
What is left of the Soviet Union in the world of "The Army is the Country" is Tajikistan.
France in the world of "The Land of Compromise" is divided and reduced into a rump state following a far more worse defeat in the Franco-Prussian War and a violent civil war. The current French government follows a "compromise" system in which it would periodically change back and forth from a republic to an absolute monarchy within a decade and the change is decided on a coin-toss. As a result, France is seen as the world's laughingstock.
Quarmall used to be a large kingdom, but by the time the eponymous pair see it, it's a single city that's almost all underground.
Likewise Lankhmar itself; in The Swords of Lankhmar, Kreeshkra mentions that "Lankhmar's empire stretched from Quarmall to the Trollstep Mountains and from Earth's End to the Sea of Monsters".
In Forging Divinity, the Xixian Empire once ruled much of the continent, but most of their lands have now been conquered.
The Galactic Empire from Isaac Asimov's Foundation novels turns into this over the course of the series, and the Roman parallels are many and explicit, including a Justinian-like reconquest that collapses in on itself. By the time of the Mule, the Empire controls only twenty agricultural worlds, having abandoned its original capital City Planet, Trantor, after the Great Sack. When the story's protagonists visit Neotrantor, the new capital, the senile Emperor Dagobert IX is under the impression that the Empire is as strong as ever, treating the Foundation as just another world within the Anacreon Province of the Empire. Interestingly, his son has no memory of the old empire, and sees being the ruler of twenty worlds as pretty impressive.
The Empire of Humanity gradually transforms from a strong star-faring empire to a weak shadow of its former self.
The Taii to an even greater extent. Once rulers of most of known space, they have been reduced to a few dozen worlds and are hopelessly behind the younger races which have arisen after the Taii Empire's collapse. Unlike the human example, the current state of the Taii is due to a devastating interstellar war fought against an equal galactic power. As the author maintains, such a conflict will inevitably result in the destruction of one of the powers and a Pyrrhic Victory for the other, for it will have lost much in the war. The once-mighty moon-sized Taii battleships still patrol much of what used to be theirs. However, this is only because the current rulers of that space allow the Taii this small favor as a testament to their former glory. Those battleships are escorted by modern warships a tiny fraction of their size but which can blast the massive Taii relics with a single volley. The author uses this as a clear example of what will happen to humanity should they enter into a such a conflict with the Czygu, an equally strong empire.
The Hands of the Emperor: The empire of Astandalas once spanned nearly five entire worlds – in the present day after the catastrophic event of the Fall it has been reduced to dominion over only its original world, Zunidh.
The Strugatsky Brothers' Hard to Be a God is set in one of those - significant portions of the the empire are independent states in all of the ways that matter, something which the Imperial nobility loathes to acknowledge.
In David Weber's Hell's Gate series, the Ternathian Empire was previously a massive empire spreading across most of the planet of Sharona (essentially an Alternate Universe of Earth). Unlike most examples, the empire was not established out of a desire for expansion but instead to secure their borders against lawless brigands and organized raiders — and every time the new borders were stabilized, more cross-border raiders and brigands appeared, forcing the empire to expand to destroy them as well. Ternathia eventually withdrew from many of its outer territories when they became too expensive to maintain control of, turning them over to local governments in an orderly, controlled contraction of their borders. Specifically, the Empire's homeland is Ireland. But the traditional capital was located in a more central location, Istanbul.
In The House Left Empty by Robert Reed, a series of EMP blasts and viruses crippled the worldwide communication grid and corrupting most databases, causing governments to effectively cease to exist, with millions of self-governed micronations popping up in their wake. The United States government still exists — the postal service is still around albeit very crippled, and people still pretend to pay taxes and file IRS reports.
Kull's kingdom (Valusia, part of said Thurian civilization) is also this. He is told he can restore some of its lost glories.
By Conan's time there are a few waning empires as well:
Stygia, an Ancient Egypt analog but filled with shadowy evil, where Set and his priests rule supreme.
Koth, a decaying expy of The Roman Empire, but with less of the "powerful, disciplined legions" part and more of the "ludicrously decadent rulers" part.
Then there is dreaded Acheron, which, despite having been destroyed almost three millennia ago, has left remnants that are still deadly to those unlucky of stupid enough to stumble on them, as ''The Hour of the Dragon" demonstrates.
In S.M. Stirling's novel In the Courts of the Crimson Kings, the Tollamune emperors once ruled all of Mars. By the time of the story they are reduced to ruling the territory around their capital at Olympus Mons, where all the old court officials and functionaries continue, though largely without actual functions.
In The Legends of Ethshar, Old Ethshar became this after a time. It once controlled a sizable continent to the south but the centuries of war against their enemy led to the original empire fracturing into dozens of squabbling countries, each claiming legitimate rule to the whole empire. The army fighting in the north decided to just use the newly captured lands to found a new nation rather than deal with that.
Imperial Russia in Malê Rising. Before the Great War, she was the largest contiguous land empire on Earth. When Russia lost, the Romanovs were consigned to only reign in the colony of Russian Eritrea, in the Horn of Africa. While most of the family, chiefly the daughters, married other princes to get away, one notable member became enamored with her new home, setting off a love affair that would see her spiltwith her exiled father.
Memory, Sorrow, and Thorn: Nabban is what happens when you go the next step beyond this — once a Rome-esque superpower, it had been in decline for some time and controlled only the core of its former territories, and then about a generation before the novels High King Prester John showed up and conquered it, making it only one province of his own empire. It's still the headquarters of the continent's dominant religion, though, and its greatest knight went on to become John's Number Two.
Melniboné from The Elric Saga, having ruled over the entire world for almost ten thousand years under the blessing of the Lords of Chaos and now they're reduced to a single island and its capital, Imrryr the Dreaming City. It is noted that its latest emperor (and series protagonist) Elric could restore much of its former power if he had a mind to.
Corum has a similar set up with two vestigial empires called the Vadhagh and the Nadragh who used to rule most of the world and were at constant war with each other. Now families live isolated in castles while the Mabden colonize the world. The Vadhagh are descended from the same interdimensional elves called the Eldren that the Melnibonéans evolved from.
In the Perry Rhodan series the Arkons are this at the beginning of the series. Several systems still pay lip service to their dominance but in reality they control only their own system. Then they are absorbed by the Terrans.
A Practical Guide to Evil: The Empire Ever Dark, vestigial empire of the drow. Once a powerful, unified empire with great cities, art and education (everyone knew the classics) and a military that could stand up to the dwarves. Then, their mages decided to pursue immortality for all drow, and things got horribly, horribly wrong from then on. By the present day, the drow have been reduced to warring clans that don't even control a city each, don't know anything about their former empire, and the dwarves see them as mere vermin to exterminate in an effort to consolidate their borders.
The Society of Red Rising once spanned from Mercury to Pluto and ruled everything in the solar system. By the beginning of the Sequel Series, The Rising and the Moon Lords have reduced it to just Mercury and Venus. And then Iron Gold opens up with them losing Mercury to the new Solar Republic.
The Reynard Cycle: The Kingdom of Aquilia has shrunk down to one third of its size, and isn't even called the Kingdom of Aquilia any more due to the fact that the remaining third split into two warring halves long before the events of the first novel. One of the antagonist's primary motivations is a desire to reunite the Kingdom, and restore the Empire.
In The Scar, agents from Armada visit a tiny island where a tiny handful of the Dying Race of anophelii — mosquito-people — are being kept isolated by the region's naval powers. Previously, the anophelii had reigned over the horrific Malarial Queendom, dominating and preying upon every race that had blood in their bodies.
The Nansur Empire in the Second Apocalypse series, which has been steadily losing territory to Fanim jihads for centuries and retains only a shadow of its former glory.
The Silerian Trilogy: The Kintish Kingdoms, which once ruled Sileria. In the past they were far more powerful, but have become overshadowed by the Valdani recently. The Valdani eventually invade them.
A slightly odd example which nonetheless fits all the above criteria is the U.S. government in Snow Crash, although in this case the "cutthroat politics" are office politics between software engineers. Power, influence and respect all withered away, so they fill the void with bureaucracy.
Slaver's Bay consists of three allied city states that are the remnants of the Ghiscari Empire, which was conquered millenia ago by the Valyrian Freehold. There is also the island city of New Ghis, which has a trading arrangement and military alliance with the three but is otherwise independent.
The Valyrians who crushed the Ghiscari were wiped out by a cataclysm known as the Doom of Valyria, leaving behind a handful of city-states to squabble over their legacy.
The once widespread nations of the Sarnori and Qaathi peoples are reduced to a single city each (Saath and Qarth, respectively).
The Patrimony of Hyrkoon was consumed by an expanding desert until only three cities remained.
The Golden Empire of Yi Ti already considers itself a remnant of the Great Empire of the Dawn which, according to legend, once ruled the whole world. Furthermore, in the present, Yi Ti is a fractured realm, with three claimants to the throne, none of whom have any real authority outside their capitals, with various princes, lesser kings, warlords, and even tax collectors having more direct power than any of them.
The Seven Kingdoms are sliding into this throughout the series. By the events of A Dance with Dragons, one kingdom (the Iron Islands) is independent, while another one (the North) is locked in a tug-of-war between the central authority (through House Bolton), the Ironborn, and Stannis Baratheon's army. Puppet King Tommen Baratheon only has effective rule south of the Neck, but discontent is brewing because of the disastrous decisions made by his mother/regent, Cersei Lannister, throwing them into further debt to the Iron Bank and allowing the Faith of the Seven to increase their clout. To make matters worse, parts of the Stormlands have been conquered by the sellswords of the Golden Company, who want to restore Targaryen rule to Westeros.
The Romulan Star Empire seems destined to become this in all realities — note that this was even the case before its destruction in the 2009 film.
In the novel verse, post Star Trek: Nemesis, the Star Empire fragmented into factions. Praetor Tal'aura and Proconsul Tomalak were able to reunite most of them, as the Federation sought to maintain peace along the borders (the Klingons "helped" by making Remus a protectorate). Commander Donatra, however, declared the worlds and fleets loyal to her independent. Between losing territory to Donatra, uprisings on the outworlds, and the damage from the Borg Invasion, the Empire was less than half its former size. It was explicitly stated in Star Trek: Articles of the Federation that the Romulans were no longer a superpower. They bounced back thanks to membership inthe Typhon Pact...only for the empire to presumably collapse again when Romulus was destroyed (though we're still a few years short of that in the current timeframe...)
In Star Trek: Mirror Universe, it happens sooner, after Romulus is destroyed early by a weapon of mass destruction. The core forces of the empire are reduced to joining forces with anti-Alliance freedom fighters in order to survive. The Star Empire is restored towards the end of Rise Like Lions following the collapse of the Alliance.
In Star Trek Online, the empire is also a shadow of its former self following the loss of Romulus. By Delta Rising it has been reduced to a handful of colonies. On the other hand, the Romulan Republic is doing very well.
The post-Endor Empire is like this, getting progressively more so as time passes. Various defeats actually led to factions led by formerly-Imperial warlords splintering off. By five years after Endor, the New Republic is in control of a majority of what was formerly Imperial space. Now and again it surges back somewhat, like under Grand Admiral Thrawn or the Emperor Reborn, but since the people behind these surges are inevitably killed, these are temporary. The one good thing Daala did was to reunite the forces under the warlords; she promptly killed off a good portion, but she did leave the still-united remains in the command of someone who knew their limits. By the time of the Hand of Thrawn duology, the weary Supreme Commander looks at the eight sectors and thousand systems they still command, the two hundred Imperial Star Destroyers, the "Preybird" class fighters they buy from he knows not where, and thinks about how the Empire once ruled a million systems, had twenty-five thousand Star Destroyers, and could afford more than one surviving major shipyard which couldn't keep up the demand for capital ships, let alone starfighters. He believes that the only way it can survive is for him to make peace with the New Republic. And he does. When, while pushing for the Moff Council to support his peace treaty, he's told that the Empire still has significant military power, Pellaeon's response is that they have just enough power for the New Republic to consider them worth destroying if peace is not achieved. Fittingly, this territory is called the Imperial Remnant by the rest of the Galaxy.
A century or so afterwards, it's the republican government that replaced it (the Galactic Federation of Free Alliances) that crumbles and survives only as the Galactic Alliance Remnant. Star Wars is cyclic about these things.
Replacing the Galactic Alliance? A resurgent Empire, partially subverting the trope. But when the Sith overthrow Emperor Roan Fel, he escapes to lead ANOTHER remnant, and the cycle continues...
The Star Wars Empire was inspired by the Foundation Empire, above.
Star Wars Expanded Universe: Even in the present setting, the Empire fractured into a number of states and fiefdoms after Palpatine's first death. Some of these remnants would eventually make peace with and become part of the New Republic, while another remnant fled to the unknown regions and became the First Order.
The Makabaki 'Empire' was once an actual unified empire but by the present of the story has splintered into a number of kingdoms with a shared ethnic and cultural identity. The empire still exists on paper and the Prime (ruler) of the most powerful kingdom, Azir, still technically holds the title 'Emperor of the Makabaki'; the other kingdoms respect the emperor's authority and will, for tradition's sake, comply with imperial orders — but only so far as they consider those orders to be reasonable requests. It's explicitly noted that if the Prime really tried to throw his weight around and force the rest of the Makabaki kingdoms to do things they didn't want to, he'd very quickly find out just how ephemeral his authority actually is.
Alethkar was another example prior to the rule of King Gavilar Kholin, having been united at least once before under the rule of Sadees "The Sunmaker", whose empire fell apart just as quickly as Sadees built it, with his mistake being that he tried to basically conquer the world and overreached in his conquests. It didn't help that keeping the Alethi Highprinces in line is a difficult proposition when most of them are prone to Chronic Backstabbing Disorder. This also is an example of how a ruler can avoid driving their country towards this trope — Gavilar ended up learning from his predecessor's mistakes, sticking to just reuniting the Alethi kingdoms under his rule and focusing on governing rather than just conquest (while having his brother Dalinar"the Blackthorn" handle border disputes and internal rebellions), and even after he was assassinated, his son was able to maintain a hold on the throne in spite of his relative incompetence, though it helps that the Highprinces were called to arms to get vengence against Gavilar's murderers and ended up getting distracted by the protracted war on the Shattered Plains through the competition for gemhearts, and King Elhokar had his uncle Dalinar (who had turned a new leaf after the deaths of his wife and brother) acting as a highly competent advisor to his nephew. After Elhokar's death, his sister Jasnah succededs him as ruler of the kingdom, and she is absolutely competent enough to continue averting this trope.
The Sword of Saint Ferdinand is a historical novel is set in the background of the Reconquista and Siege of Seville (1247-1248) by Ferdinand III. Five centuries after conquering ninety percent of the Iberian Peninsula, which allowed them to harass and pillage the few free Christian realms with total impunity, the Spanish Moors only keep some few Southern regions under their control, and are incapable of holding back the advance of the mighty Castillian army.
Talion: Revenant: The Shattered Empire, whose provinces became independent kingdoms but still have a common history and ties. The Talions were formed by one of the Emperors, and remain an international force in the wake of its fall even centuries on.
Tinker, Tailor, Soldier, Spy: Connie Sachs uses this as a reason for the betrayals and general moral decrepitude of the upper echelons of the British spy agency: "Poor dears. Born to empire, born to rule the world".
A major theme in the books is the steady decline of the world and the vanishing of ancient glories, leaving modern societies as little more than faded remnants living among the buried, half-forgotten remnants of the Elder Days. As such, this trope is very prominent.
The Lord of the Rings: Gondor has been in decline for the past one and a half thousand years, with its throne vacant, its borderlands constantly threatened by invasion, its former capital reduced to a Ghost City, and the White Tree (a quasi-religious symbol of the empire's health and favor with the de facto gods) dead. Its sister kingdom Arnor went through a centuries-long decline in the backstory until its last remnant, Arthedain, was overrun and destroyed by the Witch-king of Angmar, though its royal line survived in obscurity. This reinforces the parallelism with the ancient Roman empire: one part (Arnor = Western Roman Empire) has collapsed under attack, the other (Gondor = Byzantine Empire) subsists as a beacon of civilization built around a borderline impregnable city (Minas Tirith = Constantinople), but is shrinking and weakened by devious politics. In a subversion, the appendices cite that after the War of the Ring, Gondor grew back into power under King Elessar (Aragorn), a descendant of the kings of Arnor and Arthedain. An alliance with Rohan led by Éomer also sturdied the emerging Dominion of Men (including Arnor's old lands) as well. Nevertheless, Gondor did eventually come to a final end to be replaced by historical civilizations.
The Silmarillion: The Elves of Middle Earth were the dominant race of Middle-Earth prior to the wars against the forces of darkness (Morgoth and later Sauron) and the rise of men, which resulted in them diminishing in both number and power. By the time of Third Age, the Elves are a shadow of their former selves — all that's left of the once prosperous and extensive elven kingdoms are two city-states, one port, and what's essentially a single extended household. Even the most glorious Elven cities in the Third Age are just refuges and temporary dwellings where they wait until they can get safe passage to the Grey Havens, the port that they use to leave Middle Earth.
The Dwarves of Durin's Folk were never really a empire per se, but at their height they were an extremely prosperous kingdom containing two of Middle-Earth's grandest cities and trade routes, Khazad-Dûm and Erebor, and ruled over and inhabited almost all of the mountain ranges of northern Middle-Earth. Over the history of Middle-Earth they fall one by one, with Khazad-Dûm falling to the Balrog, Erebor to Smaug the Golden, and the holds of the Grey Mountains to wars with the orcs, leaving Durin's Folk as a wandering people bereft of influence and those two cities as grim reminders of their lost glory; the only permanent settlement left to them are the Iron Hills, originally a small mining outpost at the very edge of their realm. However, in another subversion, the efforts of Thorin Oakenshield, Dáin Ironfoot and Gimli end up restoring Durin's Folk to their former glory over the course of The Hobbit.
Tortall Universe: The old Thanic Empire, which turned into the sovereign nations of the Eastern Lands (Tortall, Galla, Tusaine, Tyra, and Maren). The Fantasy Counterpart Cultures it left indicate that it was also an equivalent to Rome.
In Vladimir Vasilyev's Treasure of the Kapitana, the Empire of Albion nominally controls much of its far-off lands. In practice, the local rulers pay lip service to the Empire, although they're a little more compliant if an Imperial frigate shows up in their port. One of the main characters is the youngest son of the current King of Albion, who is sent to the Euxine (Black) Sea to find the legendary treasury that was reportedly aboard the titular Turkish flagship sunk in a battle long ago. Supposedly, the treasure will replenish the Empire's coffers, allowing Albion to return to greatness. The King then sends his oldest son, the Crown Prince, with a fleet to find the true treasure — the secret to eternal life.
The Tough Guide to Fantasyland: The book named the trope. It's slightly larger than most of the Countries, with well-built and guarded Roads and a thriving farmland. Alone among Countries, there will be Politics in its capitol, with Senators and noble clans all jockeying for control, poisoning each other to get it. Tourists will be overcharged for goods there. Given the above, it's said they will enjoy themselves, as it's more like home. All of it's described as clearly similar to ancient Rome. Ironically, in the description itself it wasn't identified as being shrunken down from a larger influence and size, although the name obviously implies that.
The Traitor Son Cycle: Morea is an analogue to the Byzantium Empire and it's so broke that they haven't paid their Nordikan bodyguards for the Emperor in over a year. Their military technology is also badly outdated - against opposing knights in plate armour and archers with heavy warbows, they're serving up soldiers in mail armour.
Turtledove's Vilcabamba has a rump United States and Canada (combined into one country) in the Rockies, as well as a rump China, rump Russia, and rump Peru, all presumably holed up in mountain areas that the ridiculously advanced invading alien race is not interested in annexing... yet.
Almost every nation in The Wheel of Time is this, at least on the continent where most of the story takes place, due to a mysterious depopulation and the effects of repeated wars. Even the tiny city-state of Mayene claims to be ruled by a descendant of Artur Hawkwing's continent-spanning realm, and there were entire kingdoms swallowed by the Blight that were supposed to be very strong. Much of the depopulation since then could be attributed to people being killed/enslaved by raiding from the Blight. All of the major southern cities are indicated to be very large, as they have never been attacked and some (at the beginning of the series, at any rate) did not even believe that Trollocs existed.
... it's just shrunk.