The board game has a few editions, i think i only played the first one, and while it has a base mechanic very similar to diplomacy, it has a lot more.
There are 3 tracks, one of which is supply centres (castles), the other two are probably iron throne and gold... (That sounds wrong... But something similar)
You get a deck of cards, and can add a number to the strenght of you attacking or defending force (thecards have characters from the books on them, so jamie lannister might be the 4 of Lannisters in that deck) so instea of 1vs1 bounces, you can hve 1+4 vs 1+3... And when you have used all your cards you refresh the deck... But until then you will know what cards your opponent has left...
Also there are wildlings threatening tue north, and it takes a collective effort to fight them off. If nobody bothers they overwhelm the seven kingdoms and everyone loses...
Lots of nice blind auction style play, where you bet resources to take different powers...
Overall, i highly recommend it, though i haven't played it in a long while (since before i read the books or saw the show...)