Epirus 1205-1230 by Cplakidas for Wikipedia “Despotate of Epirus” licensed under https://creativecommons.org/licenses/by-sa/4.0/deed.en

(10) DESPOTATE OF EPIRUS & EMPIRE OF THESSALONIKA
(1205-1337 & 1356-1479 AD)

The last surviving vestigial state of the eastern Roman Empire, originating when the Fourth Crusade captured Constantinople in 1204 and enduring (briefly) after the Ottomans captured Constantinople in 1453.

Admittedly, the eastern Roman Empire was not in good shape before the Fourth Crusade, arguably with the fault lines of its dissolution already in place, but it broke apart entirely when the Fourth Crusade struck it a death blow – not its finest moment for either the empire or the Crusades and certainly not the smartest for the latter.

I think it’s fair to call it a death blow as the empire as such ceased to exist, with the Crusaders founding their so-called Latin Empire in the heart of the former east Roman empire around Constantinople – scattering three residual states of the empire vying as successor to it. Amazingly, the empire came back from the dead, reviving under one of those residual successor states, but like all revenants it was never the same again.

One of those states was the so-called Despotate of Epirus, so-called because that title, like that of the Byzantine Empire, is a modern historiographic convention rather than a name in use at the time.

Like the other two, it claimed to be the legitimate successor of the eastern Roman empire – and even took a decent but ultimately unsuccessful swing at it by expanding in Greece towards Constantinople, in what is styled as the Empire of Thessalonika, until their imperial aspirations came to an abrupt end with their disastrous defeat by the Bulgarian Empire in 1230.

From there it gets convoluted but essentially the original Epirus part broke away from the new Thessalonika part, before both were swallowed up again by the successor state that did go on to revive itself as the east Roman Empire – with Thessalonika being straight up reabsorbed in 1246, while Epirus bounced back and forth until its final reconquest in 1337.

Only to slip the imperial leash again in 1356 during one of the eastern Roman empire’s interminable civil wars, bouncing from Serbian dependency to being inherited by Italian rulers, until it too fell to the Ottomans – although in its case, some small parts of it endured beyond the fall of Constantinople, with the very last stronghold in the town of Vonitsa, holding out until 1479.

Shout-out to those other eastern Roman holdouts that (briefly) survived the fall of Constantinople, most notably the so-called Despotate of the Morea – which had become a tributary to the Ottomans but rebelled, prompting the Ottomans to conquer them outright by 1460 or 1461 (depending which holdout you go by).