0) An introductory "Prologue" (like the Tribes' Fury "Raven's Slaughter" in Tribes of the East). A short map that will introduce you to the mod's new features.
1) Demon campaign (5 missions) "demons grow stronger"
2) Human campaign (5 missions) "humans weaken and retreat"
3) Elemental Lords campaign (5 missions) "elementals charge in and save the humans, kicking some demon ass"
In Heroes 5, the developers introduced the elven language "Monlin" (translated as song of the earth); you can google it later if you are interested.
In this language, there is the word Shan=shadow and Mon=earth, resulting in Shanmon
The only known continent of Ashan at the time of the end of Heroes 5 Tribes of the East is "Talan" from elvish (green glade).
To the north of the Ashan map, there is a sea called the Sea of Shadows. Beyond this sea lies the continent of Shanmon (Shadow Land).
I am not an Ashan lore expert—not at all. Moreover, I know perfectly well how Ashan was conceived during the development of Heroes 5; having missed all deadlines, three Ubisoft screenwriters spent a couple of months before the game's release hastily copying world-building and history from another universe using ctrl c + ctrl v. Then, in subsequent parts, the writers tried to fix what had resulted in Heroes 5.