By 6th century, four major circles of influence had emerged in northern Britain. In the east were the Picts, whose federation of kingdoms stretched from the river Forth to Shetland. In the west were the Irish-Gaelic speaking Dál Riata with their royal fortress at Dunadd in Argyll. In the south was the Brythonic Kingdom of Strathclyde, descendants of the Roman-influenced tribes. Finally, in the south east, the “Angles”, Germanic invaders who held the Kingdom of Bernicia (later the northern part of Northumbria).
Dál Riata (also Dalriada or Dalriata) was a Gaelic overkingdom on the western coast of Scotland (then Pict-land) and parts of Ulster in Ireland. Traditionally, it has been held that Dál Riata was founded by Gaelic Irish migrants who brought with them Christianity, writing, and new technologies that were not inherent in Pictland. The inhabitants of Dál Riata are often referred to as Scots, a name originally used by Roman and Greek writers for the Irish who raided Roman Britain.
The kingdom reached its height under Áedán mac Gabráin during the 2ed half of the 6th century, when its growth was halted at the Battle of Degsastan in 603 by Æthelfrith of Northumbria. Then followed serious defeats in Ireland and Scotland that ended Dál Riata’s “golden age”, and the kingdom became a client of Northumbria by 650, and of Pictish Fortriu later on with puppet kings placed there by the overlords.
During the 8th century the kingdom was a battlefield for a series of fights between the Picts and the Northumbrians, which efficiently destroyed it. In 839 the combined forces of Dal Riatha, Strathclyde and Fortriu were crushed by Vikings. The Vikings then made a division of Dál Riata between them and the natives, with the vikings controlling most of the islands, and the Gaels of Dal Riatha controlling the Scottish coast. In turn this gave rise to the new Kingdom of the Isles traditionally established by Ketill Flatnose by 886. This division of the land with the Vikings and the fall of Pictish Fortriu in 839 lead to a short revival of Dal Riatha when Kenneth MacAlpin took the throne there in 840 and by 843 was already controlling most of Scotland in the first stages of forming the new Kingdom of Alba.