Dominions 3: The Awakening/The Eras

The Ages
Dominions 3 can be played in 3 different Eras (also known as Ages). The nations will be different in each Era. They can get era specific spells and summons, also different national troops and leaders. Not every nation is playable in every Era, as some disappear completely and others get replaced over the course of the history.

In addition to nation lineup, era also affects the frequency of different independent population types and the frequency of magic sites. Some population types and magic sites may be restricted to certain eras only and are impossible to find in other eras.

Custom map commands and/or modding can be used to set up cross-era games. Different era versions of the same nation have slightly different flags so you can tell them apart when they are playing against each other in this type of game. All nations also have a short descriptive phrase attached to their name which is different for each Era (e.g. Ulm, Enigma of Steel; Ulm, Forges of Ulm; Ulm, Black Forest).

Eras and the history of the Dominions world
Dominions 1 and 2 had several nations that resulted from the collapse of a great empire once ruled by Ermor, before it was devastated by a necromantic disaster. In Dominions 3, it appears that these events take place between the Early and Middle Eras.

Between Middle and Late Eras the starspawns of R'lyeh successfully dominate the seas and destroy Atlantis and Oceania. Oceania is eradicated, but Atlantis manages to form a new nation on land, while other Atlantian refugees appear in some Late Era nations.

List of nations by Era
Entries with a ? are unconfirmed or speculative. The rest have been seen in a screenshot or other official source.

"The original" means that the nation may be similar to its Dominions 1 or 2, no-special-theme version.

Early Era
The presence of magery is very strong in this era. Magic sites are more common and heavy armor is rare. Some (most?) nations are still in Bronze Age technology. Several nations have very powerful, and very expensive, mages. Some nations of this era have some very powerful sacred beings.
 * Abysia, Children of Flames (a bit different from Dominions 1 and 2 base Abysia !)
 * Agartha, Pale Ones
 * Arcoscephale, Golden Era
 * Atlantis, Emergence of the Deep Ones
 * Caelum, Eagle Kings
 * C'tis, Lizard Kings (the original?)
 * Ermor, New Faith
 * Hellheim, Dusk and Death
 * Kailasa, Rise of the Ape Kings
 * Marverni - predecessor of Marignon, based on Celtic tribes
 * Mictlan, Reign of Blood (the original)
 * Niefelheim, Sons of Winter
 * Oceania, Triton Kings
 * Pangaea, Age of Revelry - at a time when blood magic was still in common use
 * R'lyeh, Time of Aboleths
 * Sauromatia, Amazon Queens - the land later known as Pythium, before it became part of the empire of Ermor.
 * T'ien Ch'i, Spring and Autumn
 * Ulm, Enigma of Steel
 * Vanheim, Age of Vanir
 * Yomi, Oni Kings

Middle Era
Balanced era. The use of steel is now widespread, but magic and uncanny beings have started to fade from the world and it is more difficult to call them back.
 * Abysia
 * Agartha, Golem Cult
 * Arcoscephale, The Old Kingdom
 * Atlantis, Kings of the Deep
 * Bandar-Log, Land of the Apes
 * Caelum, Reign of the Seraphim
 * C'tis, Miasma
 * Ermor, Broken Empire
 * Jotunheim, Iron Woods
 * Machaka
 * Man, Tower of Avalon
 * Marignon, Fiery Justice
 * Mictlan, Reign of the Lawgiver
 * Oceania, Coming of the Capricorns
 * Pangaea, Age of Bronze
 * Pythium, Emerald Empire
 * R'lyeh, Fallen Star
 * Shinuyama, Land of the Bakemono
 * T'ien Ch'i, Imperial Bureaucracy
 * Ulm, Forges of Ulm
 * Vanheim, Age of Men

Late Era
This era features an emphasis on more conventional warfare. Magic is rarer and harder to find than in previous eras, but higher technology like plate armor and crossbows are more widespread.
 * Abysia, Blood of Humans
 * Agartha, Ktonian Dead
 * Arcoscephale, Sibylline Guidance
 * Atlantis, Frozen Sea
 * Caelum, Return of the Raptors
 * C'tis, Desert Tombs
 * Ermor, Ashen Empire
 * Jomon, Human Daimyos
 * Man, Towers of Chelms
 * Marignon, Conquerors of the Sea
 * Mictlan, Blood and Rain
 * Midgard, Age of Men
 * Pangaea, New Era
 * Patala, Reign of the Nagas
 * R'lyeh, Dreamlands
 * T'ien Ch'i, Barbarian Kings
 * Ulm, Black Forest
 * Utgard, Well of Urd

Nations/Themes from Dominions 1 and 2 that no longer appear in Dominions 3
Unlike most old national themes, Soul Gate and Carrion Woods are not nations in Dominions 3, but rather nation restricted global enchantments. Their unique summons have been incorporated as national summons for the corresponding nation. Marignon's Diabolical Faith theme has been merged into Conquerors of the Sea. Its Fires of the Faith theme may have been merged with the old base Marignon to create Dominions 3's Middle Era Marignon, or just dropped. Ulm's Iron Faith theme has been merged into Black Forest. Pythium appears only in the Middle Era, so the Serpent Cult theme could have been either merged into standard Pythium, used as part of Sauromatia, or eliminated; details unknown. Man's Last of the Tuatha theme is not present as a nation; it's not known if the Tuatha are still around as national or regular summons, or just gone.