The United and Divided Imperium of Granath began with the splitting of of the Ancient Kingdom of Keldar.
The Ancient Kingdom, known then as the "Absolute Kingdom" because it's borders were the coastlines of the entire continent, was split when the twin sons (Vessus and Cassus) of the 17th King, Ossus, disagreed over the inheritance of the Kingdom. Vessus was the older, and the recognized heir, but Cassus was the stronger, and both commanded great loyalty. To prevent civil war, they both abandoned the capital city.
Vessus founded a new capital on the western peninsula, and called the realm Kelden, which simply meant "of Keldar". Cassus moved into the rich heart of the eastern half of the continent, and established the kingdom of Granath, which meant "Greatest Life". He took the name "Cirath" for himself, which means "Guardian of Life". Although the capital of His Divine Majesty has long been moved, the Title of those original central lands remains Cirath to this day.
Cassus Cirath, the first High King of the Granath Imperium, did not have a free and easy hand creating his new Kingdom.
The Kingdom of Keldar originally grew out of the North of the Middle Peninsula, now known as Kord, or The Wild. The first Keldar King is said to have been a barbarian of uncommen wisdom and a gifted tongue who united all of the Middle and Western Peninsulas, then conquered the Eastern Peninsula city-states one by one, which wasn't a hard task as each had only a small militia for defense. These Eastern people were then largely left alone; there were only two ways to travel from the west to the east; a narrow land-bridge in the north and massive swamplands in the south.
To gain rapid compliance with his rule of the new kingdom of Granath, Cassus gave the title and rulership of each city state and the surrounding area to the most powerful figure in that area. To buy the support of lesser people, lesser titles were established, as well. All of these titles can be awarded by the High King and taken away, and they cannot be inherited without the High King's permission.
In the current day, most of the Kings of the individual realms of Granath are related to the High King, although sometimes distantly. Similarly, most the lesser titles can claim some kinship to their King and the High King. There are some members of the royal court who have received their title to great acts of service, or more commonly, due to political prudence. The High Crown is technically an inheritance, but with so many relatives to the throne among the ruling class, ascendancy is more a matter of political intrigue than bloodlines.