alternatehistory.com

Dál Riata. Technically speaking, Dál Riata is an overkingdom composed of numerous lesser kings under a single High King. The reality is that there are two High Kings, with one being the ceremonial head of the whole kingdom. This situation came about when, due to intermarriage with the the rulers of Airgíalla, they came to be ruled by the same king; Áengus Mac Áedán. With the combined strength of both kingdoms, and extensive use of the Dál Riatan navy, Áengus was able to conquer the neighboring kingdoms of Dál Araidi, Dál Fiatach, and Echach Cobo, and also forced tribute from the isle of Monau. He had several sons, whom he arranged marriages to across his wide kingdom. This proved disastrous as after his unexpected death, as they all fought to be the High King.

The Dál Riatan civil war came to an end six years later, when a compromise was struck. One would be king over the Eirean (Irish) part of the kingdom and the the other over the Alban (Scottish) part. The later would also be High King over the whole, but the former would always be his tanaiste(heir). This relationship gets a further twist whenever the Eirean king is made the King of Tara, and thus (symbolically at least) The High King of the Irish. Such is the case in 803.

So far at least it has not caused any unrest, but high king Fionn Mac Cináed (Fionn the 2nd) is a paranoid bastard. So much so, in fact, that he has made hostages of all the heirs of his underlings, and of his allies as well...