Trope Workshop:Land of Shattered Empire

A common element of an Adventure-Friendly World is that the setting is set upon the ruins of a now defunct empire. This allows creating a world without a central authority to solve problems, and several factions willing to wage war (either open or espionage) on one another, while maintaining several conveniences one would spawn such as a common language, and a shared history, as well as allowing for now international institutions, standards and/or road networks (which are often in disrepair and plagued by bandits, disposable or otherwise, who are often dumb enough to attack heavily armed and armored men). One or more of the factions may claim continuity with the old empire.

See also Balkanize Me, which may well happen to such an empire if it spanned a large enough collection of peoples and cultures.

Anime and Manga

 * Shin Angyo Onshi: The empire of Jushin was shattered into pieces before the series starts for unclear reasons, though it is heavily implied that Aji Tae, the Big Bad, was responsible. How exactly it happened is subject of one of the flashback arcs, and this shattering is one of the main reasons Munsu is in pretty difficult position to get his revenge over Aji Tae.

Literature

 * Star Wars Expanded Universe media set after Return of the Jedi fits here, with the New Republic and the remnants of the Empire (led by multiple independent warlords who often fight each other as much as the New Republic) fighting for control, going back and forth, with third parties often intervening. In this case, the Galaxy(yes, it is named like that in-universe) itself is an example.
 * A Song of Ice and Fire don't start like this but becomes one as the story goes on. With Robert's death, and the pretty nasty rumours that his heirs are actually product of incest between his wife and his brother-in-law, the Seven Kingdoms of Westeros begin to divide in several factions fighting for control or at least independence, with the Lannisters and Stannis simultaneously claiming to be Robert's successors, starting the War of the Five Kings. Thanks to the books having multiple point-of-views, the audience is able to see how the shattering went from several angles, and how heroes, villains, and anti-heroes and anti-villains try to attain their objectives through it all.

Tabletop Games

 * Eberron is set a few years after most of the countries that used to make up the Empire of Galifar have finally made an uneasy peace following one of them being destroyed overnight in mysterious circumstances. Galifar left behind standardized coinage and (now unenforceable) agreement of checks and balances on the Dragonmark Houses, though railways, major roads, the primary language, and many other institutions are attributed to the still extant Dragonmark Houses. Since the Five Nations can't move militarily without fear of breaking the truce, Sealed Evil in A Can and other international threats must be solved by the player characters.
 * Points of Light is set a hundred years after the fall of the Empire of Nerath. Now the mightiest factions friendly to humanity left are mere city states who struggle to project power beyond their walls and hire mercenaries to deal with all manner of external issue. Nerath has left behind vast ruins filled with treasure and a single language, and is presumably responsible for the standardized gold pieces as well.
 * A breakup of the United States creates the conditions for a lot of Sky Pirates and squabbling air powers to infest the world of Crimson Skies.

Video Games

 * The Calradic Empire of Mount & Blade has been gone for a few hundred years leaving behind several factions who all claim to have a historical right to the rest of the former empire (and thus reason to wage on/off war with their neighbors). Naturally it's up to the player to do something about this. The prequel, Bannerlord, is set just as the empire has split from a Succession Crisis and its former tributaries have broken off.
 * Paragon City, the titular metropolis in which City of Heroes is set, seems to be an example of this trope, what with all the parts of the ancient city of Oranbega that underlie it. And some players suggest that the United States as a whole may well also have been irrevocably shattered in the wake of the Rikti invasion, given how there is absolutely no federal-level response to the continued presence of the Rikti in the city, not to mention the military forces of at least two different hostile governments (Arachnos and Nemesis), and a blatantly terroristic NGO (Malta).  There are certainly enough wrecked bases and labs as well as other ruins left behind after the invasion to qualify on their own.
 * The second part of Final Fantasy VI, the World of Ruin, is set on the ruins of everything, including the Gestalt Empire. Kefka doesn't rule anything; he terrorizes everyone instead, to the point some people began to worship him as a god.
 * Final Fantasy XII: Ivalice used to be united the authority of the Galtean Alliance and the Dynast King Raithwall. The main plot involves the (significantly smaller) empire of Archadia trying to dominate the entire land all over again, with the main antagonist Vayne wanting to be called the new Dynast King.
 * Final Fantasy XV:.

Real Life
Eras that count when used for Historical Fiction
 * Post Han-Dynasty China, made famous by Romance of the Three Kingdoms and its many derivatives.
 * Dynasty Warriors series, especially the Empires sub-series which turns it into a setting for the player to form a kingdom.
 * Romance of the Three Kingdoms (the video game series).
 * The Sengoku Period of Japanese history.
 * The sister series of Dynasty Warriors Samurai Warriors and its Empires sub-series.
 * Nobunaga's Ambition
 * The Low Middle Ages
 * Crusader Kings II with DLC, and III by default.