I think it is very possible that events such as 9/11 (for those not directly affected....) can have an effect similar to a more personal bereavement, and thus can act as a trigger. I know that I, elsewhere in the world, did feel that the world had irrevocably changed then, and that can trigger thoughts of one's own mortality, what is left to accomplish, is one on the right path, etc.
I'm not saying that it leads directly to an MLC, but together with whatever else is going on it can certainly push in that direction. So if there are unresolved issues from an earlier age a huge event such as that can push it, in much the same was that the death of someone close, for example, can be the final straw.