[SIZE="5"]*Spoiler Alert*[/SIZE]
Partholons' power were beomcing too powerful,
so Morrighan allied with Cichol and wiped them out using the formors. <- so says the King of Partholons
But few of them survived and settled in at Tir Cornail
It is at this point Caliburn fell into the Formors' hands.
After the fall of Partholons, Nuadha along with the Tuatha came to Tara
and so started the war between the Tuatha and Formors.
EDIT : Humans, aka Tuatha's originally lived in Erinn
But when the Tuatha's were starting to loose the war, Morrighan Betrayed(?) the formors and lead the Tuatha to Tir Na Nogg
while sealing the path between the two worlds sacrificing(?) herself on the process. Thus the Formors were stuck in Erinn(the current Tir Na Nogg)
With this event Morrighan began to be called "The Goddess of Betrayal" amongst Formors.
-info from Mabinogi Guide Book(2010) - Erinn History
The question is when does Vindictus take place at.
Is it BEFORE or AFTER the switching of Erinn and Tir na Nogg.
EDIT(2) : So Tir Na Nogg(now known as Erinn) is homeland to the Formors.
Pretty good reason to be Pi$$ed off at humans IMO