What Caused The Timelines to Shatter?

I don't actually own Shattered Timelines yet, although I'm planning to get it soon.  I was just wondering if there is any explanation given for the timelines colliding? Thanks.

There are tons of working theories out there. It has yet to be explicitly stated in an official capacity though.

In our most recent story discussion thread on the Dreamer (a villain from the ST expansion), there was some talk about the Time Cataclysm being a result of the Dreamer awakening/being saved at the end of the Nightmare World crossover, mostly because the Iron Legacy storyline and LaCapitain do not seem to happen until after Nightmare World concludes. That plus the art for the card "Fixed Point" (from the Time Cataclysm environment in the ST expansion) point at the Dreamer being very much related to the whole thing. This is all fan speculation however.