Déisi Tuisceart

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Déisi Tuisceart was a generic term to describe a number of unrelated, rent-paying vassal tuatha (a people, or nation) on the island of Ireland, situated in north-east Munster, mainly at and south of the present-day city of Limerick. They included tuatha such as the Alltraige, Corco Baiscinn, Dál gCais, Eile, Muscraige, Uaithne, Ui Fidgente, and possibly the Mairtine.

In early historic Ireland they were subjects of the Eóganachta, who were kings of Munster. However, in the seventh and eighth centuries, under the leadership of the Dál gCais dynasty, they moved north and annexed Tuadh Mumhan Thomond as the overkingdom of the Uí Fiachrach Aidhne fell into decline. Up to this time it was part of the overkingdom of Connacht; it remains part of Munster to this day.

Thomond was to remain the heartland of the Dal gCais and its septs; it is most especially associated with the family of O'Brien (Ua Briain, Ó Briain), who reigned as its kings from the 930's to 1543, and from 1543 to the present day as Baron Inchiquin. The current incumbent (18th Baron Inchiquin) is Conor O'Brien; a thirty-second generation descendant of Brian Boru, he is also known simply as The O'Brien, and is Chief of the Name, Prince of Thomond.