Empire Four Kingdoms Game of Thrones
Feudal hereditary absolute
The Seven Kingdoms is the name given to the realm that controls most of the continent of Westeros and numerous offshore islands, ruled by the King of the Andals and the First Men from the Red Keep in the city of King's Landing. Its name dates back to the time prior to the War of Conquest, during which seven independent kingdoms existed in the continent. The realm actually consists of nine distinct regions, the remaining two being formally established after the Targaryen conquest.
The current War of the Five Kings, however, has caused The North and the Iron Islands to secede and rebuild their respective independent Kingdoms, putting the Seven Kingdoms at risk of losing some of its former dominions.
When Aegon I Targaryen embarked on the conquest of the continent from his seat on Dragonstone he had to contend with seven independent realms. These were:
With the aid of his dragons, Aegon managed to conquer all of the kingdoms, except Dorne, which would join with his dynasty through marriage a century later. Houses Stark, Lannister, and Arryn, which bent the knee to Aegon, were allowed to maintain their domains, no longer as Kings but as Lords Paramount of their respective regions - the North, the Westerlands, and the Vale - and Wardens, subject to the authority of the King.
With House Hoare eliminated, the kingdom ruled by Harren the Black was divided, with the people of the Iron Islands choosing House Greyjoy as their rulers, the lands surrounding the Trident awarded to House Tully as Lords Paramount of the Riverlands, and the lords of the lands surrounding the new capital of King's Landing as direct vassals to the Iron Throne.
House Gardener was also obliterated when King Mern IX perished at the Field of Fire. Mern's steward, Harlen Tyrell, surrendered Highgarden and the Reach to the Targaryen conqueror and was thus appointed Lord of Highgarden and Warden of the South.
House Durrandon was extinguished in the male line when King Argilac was killed by Orys Baratheon in battle. As a reward for his loyalty, Orys was granted Argilac's domain, as well as his daughter. Thus House Baratheon, Lords Paramount of the Stormlands, was created.
The only one of the Seven Kingdoms not conquered was Dorne in the far south, whose lords learned from the mistakes of the other kings and refused to meet Aegon and his dragons in open battle. Dorne retained their independence for almost two more centuries before joining the realm through a dual marriage with the Targaryens.