Dragonstone, sometimes referred to as the Kingdom in the Narrow Sea, is a faction located east of Kings Landing on three Islands and two Peninsulas in the Narrow Sea. It is ruled over by King Stannis Baratheon. It's main city is Dragonstone.
Dragonstone is the smallest of all the factions contending for the Iron Throne. Dragonstone's largest advantages is it's location in the sea, bottlenecked Peninsulas and it's heavy units that can defeat most other faction's in a seabattle. Dragonstone's victory relies heavily on quick land grabs and the larger factions distracting each other.
Dragonstone and it's two other islands were given to Stannis Baratheon following the Baratheon victory in the War of the Usurper. After Stannis declared war on the Iron Throne many Crownlander Lords joined his cause. Such as Ser Justin Massey and Lord Roger Staunton.