This is low-fantasy fictional history at its best. Lots of battles, doublecrossing, backstabbing, machinations, and just plain dumb luck turning the tides of war.
King Aerys was mad, and he was overthrown by an alliance of the Starks of Winterfell, the Lannisters, the Baratheons, and other great houses. Now some of the families are scheming to replace King Robert Baratheon.
In addition to the Machiavellian doin's of the Houses, Winter is coming. Winter comes once every great many years, and with it come the wights and the Others from the North, beyond the great Ice Wall (which is guarded by the Brothers in Black -- basically a group of criminals and political exiles tasked with guarding the Wall as penance).
Note: these books are *rough*. People die quite a bit in sometimes nasty ways, and as Thane told me, don't get attached to anyone. I'm half way through the third book and that admonition was just wickedly brought home with a particularly nasty piece of work. Fortunately there are a lot of characters (all very well done), so I'm confident that someone will be left at the end. :-P
Some of the best fantasy I've read in a long time. Recommended in spades.