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During Donnchadh's time the great feuds that had been causing war on the western seaboard of Scotland since Somhairle mac Gille Bhrighde were coming to an end. Ruaidhri mac Raghnaill, son of Ragnall mac Somairle, King of the Isles and Lord of Argyll, was at peace with Raghnall mac Gofraidh, King of Mann, and had become friendly with Ailean mac Lachlainn, Lord of Galloway and Constable of Scotland. In this context, Alexander II, the King of Scotland, led expeditions into Argyll in 1221 and 1222, expeditions which led to Donnchadh being recognised or appointed to the Lordship of Lorne. Donnchadh remained a strong supporter of the Scottish crown against the interests of Ruaidhri mac Raghnaill and Amhlaibh Dubh.
These expeditions into Argyll appear to have given Donnchadh domination of the kindreds of all Argyll in place of Ruaídhrí. Around 1225, Donnchadh de Argadia ("of Argyll") appeared in a charter of Maol Domhnaich, Earl of Lennox (d. 1250) made to Paisley Abbey; this appearance is notable because it is the first attestation of the locative family name "of Argyll", the name that Donnchadh and his descendants would use to identify themselves among the higher nobility of Scotland.
In 1229, the Manx king, Raghnall mac Gofraidh, was killed. Fear of Galwegian or Scottish royal intervention led the Manxmen to appeal to the Norwegian crown. The Norwegian expedition, led by Óspakr-Hákon, probably Donnchadh's brother, ravished Kintyre and in 1230 attacked the Stewart controlled Isle of Bute. This expedition was unsuccessful and led to Uspak's death. Donnchadh remained firmly in possession of his Argyll lordship.
The Mormaerdom or Kingdom of Argyll was also a lordship in High Medieval Scotland.