One of many ways to think about it is that there was always some chaos lying around, but the Arkat-Nysalor conflict went through phases where each side escalated its "magical technology." Think of it like an arms race that ultimately ends in one side discovering biological or nuclear weapons and using them extensively. Where chaos was previously dormant and opposed, you now have someone actively exploiting it. Where the analogy fails, like all analogies do, is that nukes don't have minds of their own, where chaos does.
Chris Lemens