Fantasy Counterpart Culture: Carthage. Which is also the reason for their disappearance in later ages: they get destroyed by Ermor (the Rome-counterpart)note and admittedly Machaka in between the Early and the Middle.
Crystal Dragon Jesus: Only in the Early Age. In the Middle Age the bishops of the New Faith were replaced by the Thaumaturgs of the Death Cult.
Dark Is Not Evil: Sceleria in Dominions 4. A Middle Age splinter of old Ermor, it was founded by the last Ermorian Emperor's twin brother and the Thaumaturgs. Their creed involves raising the dead to serve the living, and they do (mainly by raising skeletal legionnaires to fight against Ermor).
Dem Bones: In the Middle Age, Ermorian priests can raise skeletal legionnaires as part of its army. In the Late Age, the dead will rise on their own, but you need a fortress in order to get the decent units.
This was changed in Dominions 4. There, Sceleria (an Ermorian splinter state founded by the Thaumaturgs of the Death Cult and the last Emperor's twin brother — it's pretty much previous games' Middle Age Ermor given a more positive spin) can have its priests raise skeletal legionnaires as part of its army in the Middle Age, while Ermor is the dead realm of previous games' Late Age. There is no Ermor in the Late Age, and the closest thing to it (Lemuria, the Scelerian successor) has the dead rise on their own in spectral instead of osseous form.
The Empire: While all pretender-ruled states fits the trope, early Ermor in Dominions 4 is the state that backstory-wise fits clearly here, with three Middle Age states confirmed as descended from the occupation of Early Age nations (Pythium from Sauromatia, Marignon from the Maverni, Ulm from Ulm), another splinter state carrying on the traditions of the old Ermor (more or less — Sceleria), the heartland of Ermor itself being the centre of an undead realm, and the reason for another of the disappeared Early Age nations (Berytos) is that Ermor smashed them.
Necromancer: In the Middle Age Thaumaturgs and cultists are able to reanimate the dead.
Night of the Living Mooks: Middle Age Ermorian priests are can raise a sizable undead army. In the Late Age, the undead rise on their own.
Start of Darkness: Thanks to it's wizards studying C'tisian death magic, Middle Age Ermor is a desolate wasteland of the dead, and Sceleria has been forced into an uneasy compromise to keep Death from breaking loose.
Heel-Face Turn: Ashod abandons the blood magic of Hinnom, its giants' hunger has faded to the point where they're no longer cannibalistic and they can summon a variety of celestials (though they still practice slavery). By the time of Gath the blood cult is back, but there's also a new cult based on guiding and helping humans.
Humanity Ensues: The number of giants dwindles with every era and human immigrants gain greater prominence.
Virgin Sacrifice: Which makes for an interesting parallel with the Word of God-mentioned successor nation: Marignon (Ermor conquered them and evidently had a greater impact on their national identity than Ulm, thus the name-change).
Crystal Dragon Jesus: The Theurgs of the Middle Age. By the time of the Late Age, they've been pushed to the side by the Serpent Cult, as well as several minor cults suck as the Cult of The Solar Bull, a Crystal Dragon Mithras, and the Cult of the Great Mother, Crystal Dragon Cybele.