Ferelden is a relatively young kingdom located in southeastern Thedas. It was formed by King Calenhad nearly four hundred years before the start of the Fifth Blight by uniting Alamarri clans.
The nation was invaded by Orlais in 8:24 Blessed and fully conquered 20 years later. For the next 78 years it was under Orlesian occupation. Orlesian noble Meghren was installed as the king of Ferelden during the late years of the occupation, and the Theirins were forced into hiding while keeping alive the rebellion.
Ferelden was freed through the efforts of Maric Theirin, who was the rightful heir to the throne, and a commoner, Loghain. Loghain and Rowan Guerrin defeated two legions of chevaliers sent to support Meghren at the Battle of River Dane, forcing Emperor Florian to withdraw all support for Meghren. Eventually by 9:2 Dragon, King Meghren and the remnants of his court fled to and barricaded themselves inside Fort Drakon. Maric challenged Meghren to a duel and killed him in single combat, ending his rule and the Orlesian occupation. Maric then married Rowan and set out to rebuild Ferelden.
Royalty
The King is the most powerful noble in the kingdom. Although Denerim was originally the official "teyrnir of the King", it has since been changed to a separate noble's arling, as the king's domain is all of Ferelden. However, even the monarch's power must derive from support throughout the land. The sight of a King asking for, and working to win the support of, "lesser" nobles is a source of constant wonder to foreign ambassadors.
Teyrnirs
In antiquity, Teyrns arose from among the Banns, having grown powerful enough to move lesser Banns to swear fealty to them. There used to be many more teyrnirs before the rise of Calenhad, but he downsized them during his war for the throne. In modern Ferelden there are only two teyrnirs; Gwaren in the south and Highever in the north. Teyrns are still owed fealty by vassals of both Arl and Bann ranks, whom they may call upon in the event of war or disaster. However they are also responsible for lending aid to them when needed. In modern times a king or a queen has the right to name a teyrn.
Arlings
The Teyrns at some point established arlings, giving the title of Arl to those assigned to command strategic fortresses that the Teyrns could not oversee directly. Arls are more prestigious than Banns, but they usually have no Banns sworn to them - known exceptions being Amaranthine and South Reach.
Bannorns
Each freehold chooses the Bann or Arl to whom it pays allegiance. Typically, this choice is made based on proximity of the freehold to the lord's castle (as it's rarely worthwhile to pay for the upkeep of soldiers who will arrive at one's lands too late to defend them). For the most part, each generation of freeholders casts its lot with the same Bann as the previous generation did, but things can and do change. No formal oaths are sworn, and it is not unheard of, especially in the prickly central Bannorn, for Banns to court freeholders away from their neighbours - a practice tending to ignite feuds that can last for ages.