What Significance Does the Number 7 Have on Game of Thrones?

The Seven Kingdoms make up the realm of Westeros, i.e., everything everyone wants to rule. These are the seven major kingdoms and the houses and/or regions associated with them:

1. The North (House Stark/Winterfell)
2. The Mountain and the Vale (House Arryn/the Eyrie)
3. The Isles and Rivers (House Harrenhal)
4. The Rock (House Lannister/Casterly Rock)
5. The Stormlands (Storm's End)
6. The Reach (Highgarden)
7. Dorne (House Martell/Sunspear)