Ok.... Number one:
Alric, Cu Roi and Murgen don't "Join" the legion. They were already part of the nine and already "joined"..
Number 2: King Caliban was the leader of the west. He gave his power to The Nine. Remember the archer flavor text?
"The truce in which the fir'bolg were brought into the light was forged by King Caliban and the great King ou'kahn during the SWORD AGE"
The SWORD AGE is when Myth takes place. Caliban was probably killed when Madrigal was sacked (when Alric was campaingning in the east)
Rive