I don't believe in motives other than ''power'' or ''I hate everyone'' because that's really what most things boil down to in the end. :P
For instance, Louis XIV of France centralised his power by forbidding the Hugenots (the protestants in France, it's what we call them here) which was basically a power motive because he wanted more power by having 1 faith, which would allow him to do stuff through the church.

It still meant he'd kill everyone because fuck you you protestant douche!