Confusing Bioshock 2 Story (Spoilers)

Could someone please explain the story of bioshock 2. I've beaten the game once and save most of the little sister's. Somehow, I managed to get through the whole game and not understang what was going on. If anyone could explain, it would be greatly appreciated.

i havent completed it yet so i dont really know. i kinda like the game but its not really sucking me in atm. im pretty disappointed.

Understang=Understand Sorry

Is there anything in particular u dont understand or is it the entire thing?