Justice League of America: Dark Things

I'm not as up on my Justice Society of America things as I should be to really follow this volume.  In fact, I didn't realise it was a cross over until about halfway through when I was wondering why everything started repeating itself.  Dick continues to build his Justice League to include a speedster (Jesse Quick) and a Green Lantern (Jade) and I like the way he views things but I was a little lost on the history here.