Heroes II backstory.

Didn't Archibald tear Erathia apart (and then, of course, died and became a necromancer)?

Well, it seems that Sandro tore Erathia apart when he gave Haart the poison for the king, and the king subsequently died. Then Vilmar imprisoned Sandro and resurrected Griffonheart as a lich. He (Griffonheart) seized power. Then, the dark mages from Nighon and the demons from Eofol declared war on Erathia. And then Catherine arrives, and "The Restoration of Erathia" begins.
And Archibald didn't die; after the wars for the throne, he was turned to stone and placed in the library. Then, some heroes decided to save the world from Krigan (Might and Magic 6) and revived Archibald. He gave them a scroll and then disappeared. He appeared in Erathia as the ruler of the Abyss and De'i, but then he was overthrown by Castor, and Archibald went with a group of necromancers to the Tularean Forest, to Clanker's laboratory. Then he learned about Roland, who was languishing in the ZOD colony, and asked the lords of Harmon'dale to save his brother and gave them the weapons of the ancients. Then he brought his brother to Catherine and asked for forgiveness, and in the end, he was exiled forever to Clanker's laboratory, where he continued to practice necromancy