When it happens, it won't be a specific event. It'll be the collapse of infrastructures built on foundations that are simply not up to standard but were allowed to happen anyway. Whether that be economical, public medical, one of the many sciences, or all at once.

People will die and it'll be tracked back to haphazard slop five years earlier.

Edit: No, not haphazard slop. Just some idiot that thought it was all magic at the time.