This nation used to rule the known world, or at least a sizable chunk of it. Unfortunately, for the last n years, this nation ended in the last stage of The Cycle of Empires as its influence has been declining and its territory shrinking; the lands that previously were firmly under their thumbs being either snatched up by opportunistic neighbors or invading outsiders who saw the chance to take their old enemy down a peg, or gaining independence at the hands of separatist movements smelling the weakness of their overlord and deciding that the time is ripe to claim their right to self-determination either through political means or open rebellion. The erstwhile Voluntary Vassal is now neither voluntary nor a vassal.
Vestigial Empires tend to leave behind still-working infrastructure, especially roads, bridges, ports, and administration facilities, as they shrink (for a Space Opera, they will leave behind the space equivalent, like spaceports and launch pads). Frequently, they also leave behind a Common Tongue, an educational system, laws, cultural traditions and rituals. For this reason, even if the senate and army are disbanded, vestiges of the empire's influence persist. Generally their remaining vestiges of control are a hotbed of cutthroat politics, ruled by unstable alliances of decadent nobles with superiority complexes and equally decadent and morally challenged courtiers. Backstabbing and betrayal are the path to temporarily grasping power. In space, this may result from an Ungovernable Galaxy.
The protagonist is rarely actually from the Vestigial Empire — any time one is involved in a setting, it's usually either a source of villains, or a setting whose politics need to be navigated in order to obtain allies. Quite often, the only mention of them may be in a Cryptic Background Reference. However there are exceptions; if a protagonist IS part of a Vestigial Empire then expect him to die in a Last Stand, lead The Remnant to found a successor state, or simply try to protect himself and his family as civilization falls apart.
Being a Fantasy Counterpart Culture to late Imperial Rome or Byzantium isn't required, but it's definitely a bonus.
Compare with Failed State, wherein a nation's government collapses to the point where it is unable to exercise executive control, run any government programs, or enforce any laws. In contrast, in a Vestigial Empire, even when it loses control over its far-flung empire and its armies wither, a core of executive and administrative infrastructure (albeit with little or no power) is often left behind by the Vestigial Empire as it draws back its influence. Contrast with Precursors — an entire species of Vestigial Empire which tends to leave little to no working infrastructure and is also long gone by the time the story takes place. All or part of the Vestigial Empire may be The Remnant if they're still fighting for the (usually) lost cause of restoring their former glory.
Over a long enough time period, the Vestigial Empire is likely to result in Look on My Works, Ye Mighty, and Despair. If a Vestigial Empire actually DOES succeed in restoring itself to its former glory, then that counts as Resurgent Empire.
An inversion is a Rising Empire.
- Attack on Titan has revealed that the Walls are in reality the last bastion of the once proud Eldian Empire, formed by Eldians led by the royal Fritz family. They settled on the island of Paradis as the Kingdom of Marley overthrew and exiled them.
- Marley itself is slowly becoming this, as new weapon technology means that the Titan Shifters they've relied on for so long are no longer as powerful against their enemies as they once were. However, in order to get the rest of the world on their side and retain their position of power, they've declared war on Paradis Island in the hopes of wiping out the Eldians once and for all so that they're free from the threat of being overthrown, as there's been a constant power struggle between Eldia and Marley for almost two thousand years.
- In the ending, every country becomes this due to Eren masterminding the apocalypse. Decades later, Paradis manages to make it to the information age, but is bombed into submission and vestiged once more.
- The Planet Trade Organization, Frieza's empire, has become one by the time of Dragon Ball Z: Resurrection 'F' and Dragon Ball Super. At its peak, it controlled about 70% of the universe. After Freeza's and Cold's deaths, the empire lost most of its territories and Sorbet is barely holding the last pieces together when he decides to revive Frieza out of desperation. When the resurrected Frieza tries to get revenge on Goku, the last remnants of the army are wiped out. After the end of the Universe Survival saga, Frieza decides to rebuild his empire.
- The Beelzenian Empire in the Evillious Chronicles franchise is an example of this as the centuries go on, losing larger and larger chunks of territory until it's only a shell of its old self. Before its decline it had also conquered pieces of the (offscreen) Tasan Empire, a second example of this trope.
- The Earth Federation from the Universal Century universe of Gundam is this, in a pattern that echoes Gibbon's Decline and Fall. The Federation won the One Year War in Mobile Suit Gundam through superior power and production capability, but at the cost of half of the world's population. Seven years later, in Mobile Suit Zeta Gundam the Earth Federation has weakened to the point that the remnants of Zeon are still a serious threat, and a State Sec organization is intentionally sabotaging the Federation from within so that they can take over. Afterwards, in Mobile Suit Gundam: Char's Counterattack, even though Zeon has been defeated twice already, the Earth Federation is so weak that the Neo-Zeon is able to mount an attack that nearly makes the Earth uninhabitable. By the time of Victory Gundam (60 years after CCA), the Federation is so weak and ineffectual that it falls to a militia to oppose The Empire. Despite all of this, however, the Earth Federation is the eventual victor in each of these conflicts, if only through outlasting the various threats to its survival. If the live-action film G-Saviour is canon, then the Federation finally collapses around UC 200, when the Colonies finally achieve independence and form a new government together with the Earth, but this time with the Colonies (renamed "Settlements") as equal diplomatic partners. Not that this new government is any better than the Federation ever was.
- In Hetalia: Axis Powers, the now dead countries of Ancient Greece, Ancient Egypt, Rome, and Germania play this role, with Rome being the prominent one. He left two (idiotic) grandsons behind who are constantly being fought over because of their grandfather's inheritance, Germania is the father/grandfather of the Holy Roman Empire, Germany, and Prussia, and Ancient Greece and Egypt each left behind a son who spend a great deal of time discovering and researching the ruins of their mothers' kingdoms. Rome even comes back from heaven occasionally to check up on N. Italy and bother Germany. And if history's any indication, this may apply to Austria as well, who, as both the Austrian Empire and (one half) of Austria-Hungary, served as a remnant of the Holy Roman Empire.
- The Galactic Empire in Legend of the Galactic Heroes, as not only the government's influence is waning due the conflicts among the High Nobles, but a string of incompetent military commanders led to multiple defeats against the Free Planets Alliance, that at one point would have been able to march all the way to the Imperial capital (the one thing that saved the Empire was the death of the Alliance admiral who inflicted that defeat, as his subordinates couldn't agree with each other long enough to do it and the Alliance government lacked the political will, giving the Empire time to rebuild their military and put a gigantic space fortress on the invasion route). By the time of the series, the Imperial government is so weakened that Reinhard von Lohengramm was able to wipe out the High Nobles and impose himself as the Prime Minister and then become emperor, at which point the Empire is reformed and enters a new golden age.
- In Lyrical Nanoha, Ancient Belka was a powerful empire that spanned many dimensions, a mighty civilization that conquered every world that came its way with its superior magic and technology. However, infighting mixed with the Lensman Arms Race and widespread pollution have destroyed the empire from the inside until it finally fell apart after the self-sacrifice of the last Saint King, Olivie Segbrecht. All that's left of the Belkan Empire in modern times is the Saint Church Autonomous Region in the Northern Mid-Childa, although the Saint Church focuses more on the religious than political power (their doctrine is based around Olivie as the messianic figure) and preservation of the Ancient Belkan cultural and magical heritage.
- The Anglo-Saxon Kingdom in Britain during Vinland Saga, being constantly invaded by various Norsemen. Askeladd even discusses this with Thorfinn, bringing up the Roman Empire and all it's glory and advancement that led it ultimately into destruction, saying that it is the same now for the Kingdom of the British who contributed to the Roman downfall. Neatly enough, Thorfinn chucks away a Roman coin he picked up in the ruins (naturally Roman) they were standing in, since it was worthless to him.
- Beast Wars: Uprising: By the time the story begins, the Autobots and Decepticons have been reduced to this thanks to humanity becoming utterly fed up of both sides, and hemming them in an "Allowed Zone", which consists of Cybertron and the planet Elba. Neither faction has taken this incredibly well. By the end of the story, it's implied the same is going to happen to humanity soon enough.
- Legends of the Dead Earth: In Legion of Super-Heroes Annual #7, the United Planets collapsed after Earth was destroyed. In the 75th Century, the immortal Wildfire is the only surviving original Legionnaire. He has established a new Legion on the planet Rimbor which abides by the laws and customs of the United Planets. The former UP member states do not trust each other as a planet-sized cannon reappears to destroy a star every 100 years, which has the effect of blocking communication throughout the galaxy. Wildfire and a newly trained, highly efficient group of teenage Legionnaires are able to destroy the cannon when it appears 97 years ahead of schedule. As a result, communication is restored and the United Planets is re-established at Wildfire's urging. However, Legionnaires Annual #3 reveals that the United Planets no longer exists in the 100th Century, suggesting that Wildfire's initiative was ultimately unsuccessful. DC One Million says that the United Planets has been mostly replaced with a government called the United Galaxies. The UP still exists but consists of five of its member planets moved to one solar system.
- In Superman: True Brit, The Batman mentions working for the good of the British Empire. Colin mentions that the British Empire no longer exists but The Batman says they still own a bit of Ireland.
- Three takes place in Sparta, seven years after the Battle of Leuctra that forever destroyed the legend of Spartan military supremacy in Greece. Though Sparta was still a reasonably strong state, and had not yet decayed to the glorified tourist trap it would become under the Romans, a major part of the story is that the balance of power that holds Sparta together—the total dominion of the Spartiates over the helot slave class—is fraying at the seams, which motivates the nation's leaders into throwing everything they have at quashing a handful of escaped slaves.
- In Apocalypse Now Redux, the declining might of the French Empire is discussed by the French plantation owner, who is ready to defy the defeat streak with a Last Stand at his home, if it comes to that.
- At the beginning of Man of Steel, Kryptonian civilization is a shade of its former self, with its past glory of space exploration and colonization long gone.
- Star Wars: The Republic as seen in the Prequel trilogy is a shadow of its former self with the system being controlled by corrupt senators even before Palpatine becomes Supreme Chancellor. By Episode II, it's a democracy in name only and by Episode III, it's a fully-fledged military dictatorship until Palpatine officially renames it the Galactic Empire.
- The National Wrestling Alliance once had an iron grip on almost the entire industry, excepting a handful of "Independent" enterprises (allowed to exist to avoid anti trust legislation), "Outlaw" territories (who operated in defiance of it), and the whole of Europe (where promoters collectively refused to join until their own problems made the offer more appealing). After TNA's exodus from NWA, maintaining tentative oversight of independent promotions across a mere six countries became a challenge. But the NWA pressed on, got a temporary foothold in Europe, and remained a mostly respected presence (especially in Japan).
- Within the NWA itself, Pro Wrestling ZERO1 was one of Japan's premier promotions and was in the process of expanding to other nations by setting up off shore branches in them. But it shrank to a largish "indy fed" with a few foreign affiliates after the death of its founder, Shinya Hashimoto. It soldiers along, though, and has also joined some of the other alliances that have sprung up since the NWA's decline.
- While not as dramatic as the NWA, the Toryumon "university" system successfully bridged IWRG of Mexico and the lucharesu feds of Japan. Then a schism between headquarters of the two regions basically caused all the Japanese presence to be taken by Dragon Gate. While Toryumon Mexico stuck around and even did pretty good gates, it ended up running shows much less regularly, and its students had to figure out their further education themselves as DG had little interest in them. As Dragon Gate grew, it decided to channel its expansion into the English market, but DG USA and DG UK, its foreign branches, failed to grow like the origin branch and the DG empire crumpled faster than Toyrumon's, though Dragon Gate remained stronger in Japan than Toryumon did in Mexico.
- In the BBC series Earthsearch, the Solaric Empire is now just a few mined-out moons and asteroids populated by the descendants of the colonists who chose to remain behind when Earth was taken to another solar system to escape the sun going nova. On encountering the protagonists and being told there's an actual Earth out there (long since regarded as a myth), Grand Emperor Thorden immediately realises the potential of a resource rich planet where you don't have to live underground or in a Domed City, and starts scheming to seize their spaceship and conquer Earth for himself.
- Girl Genius: After a two year Time Skip, the Wulfenbach Empire, or Pax Transylvania if you prefer, is said to no longer exist, though it still holds a fair amount of territory and influence and has the area around Mechanicsburg locked down. After the disaster at Mechanicsburg, Europa is in complete chaos, various Storm King and former Storm King factions are either rebelling against them or trying to work with them to piece Europa back together, and the Other's forces are active again. Wulfenbach is still the strongest power in Europa, but how much territory they have left is unclear.
- Avatar: The Last Airbender shows us Chin Village. Three-hundred years before the series, the Earth Kingdom (except for the capital Ba Sing Se) was grabbed under the boot heel of Chin the Conqueror. When he died, his empire imploded, leaving only the teeny-tiny Chin Village.
"We used to be a great society! And now look at us!"
- By Season 2 of Wander over Yonder, Lord Hater's empire, which was a Galactic Superpower in Season 1, has lost a large chunk of its territory thanks to Hater's Villain Decay, causing him to go from the galaxy's supreme Galactic Conqueror to the "twenty-ninth greatest." Much of the season revolves around his attempts to get back on top.