In order to realise the amalgamation of the Kingdom of Strathclyde with that of the Kingdom of Alba, an understanding of the political events preceding it is required.
The Scotland of the sixth century was a land of four distinct peoples:- the Britons of Strathclyde; the Scots of Dalriada; the Picts of Caledonia; and the newcoming Angles of Northumbria who advanced into the Lothians.
The Britons for the most part tolerated the Scots of Dalriada. They seemed an ideal buffer and diversion to the war-thirsty Picts. An Ard Righ was quickly established but, probably due to the internal politics of the family branches of the Scots, lapsed in the middle to late sixth century. Thereafter the Scots became unpredictable and expansionist neighbours.
The kingship of Dalriada was to last around 350 years and in that time the Cenel Gabrain branch of the family became predominant. In the eighth century the arrival of the vikings convinced many kings to try and increase their powerbase. Various Dalriada kings had tried to encroach Pictish lands before Kenneth, son of King Alpin, married into the Pictish Royal line and became the first King of Alba; Dalriada and Caledonia combined. He crushed Pictish opposition to his kingship by murdering the seven Pictish mormaers, and was coronated in Scone on the Stone of Destiny. The political importance of this means that Kenneth mac Alpin is considered by many to be the first King of Scotland.
The Picts were an ancient race. Their legendary kings go back at least a thousand years before those of Dalriada, beginning with a King Bruide Pant. A warrior race, they harassed the Romans, Britons, Scots and Angles. Their kingship may have been based on matrilinear succession which led to the merger with Dalriada. When in 839, the vikings killed their king, Eoghan mac Oengus, it led to Kenneth mac Alpin unifying the crowns.
Politically, the Britons were now at a disadvantage.It may have been a flexing of British muscle when in 849 King Artgal burnt down Dunblane, but the British powerbase effectively ended after 870 and the seige of Al Cluith by Olaf the White. Artgal was captured and killed and King Constantine I of Alba's brother-in-law Run is placed on the throne. This marks a trend of British kings sympathetic to the Alba crown. King Donald II of Alba later banished the British royal family to Wales and Strathclyde found itself under direct Scottish rule. The kingship was again revived in 908 although it remained under Scottish control till final absorption in 1034.
To stay and fight would have been foolhardy for the British royal family. The Angles in the east were also looking to merge with the Britons. They had been a constant sore since the sixth century, expanding into the Lothians from Northumbria (Bernicia). Thus the exploits of King Arthur who heroically gave the British victory. The collapse of the Ard Righ gave the Angles another chance and they succeeded in taking the Lothians displacing the native British tribe, the Gododdin, who fled to Wales. The Battle of Ardderyd won by King Ryderrch Hael ensuring the survival of Strathclyde was only to prove a temporary respite. In 613, the Battle of Chester severed Strathclyde from Wales, and in piecemeal fashion the Angles later took parts of Cumbria (Rheged) from Strathclyde.
The Angles not only fought with the Britons but also with the Scots and Picts. In 603, the Angles defeated King Aedan of Dalriada at Degastan. The Picts were another matter. The defeat of King Ecgfrith of Northumbria at Nectansmere in 685 by King Brude mac Bili of the Picts effectively checked the advance of the Angles in Scotland. They tried again in 698 but were again defeated. In 711 they managed to secure a victory, thus effecting a peace between the two kingdoms for a time.
The arrival of the vikings proved a battle they could not win. The vikings raided the east coast of England with gusto, establishing a base at York. In 867, the Northumbrian kings became sub-kings under Norse rule. The kingdom was eventually reduced to that of an earldom and much reduced in power.
Tom Begg's The Kingdom of Kippen notes: "For at least seven centuries, however, the northern boundary of the British kingdom of Strathclyde was the southern flank of the upper Forth valley and the Kippen promontory was literally on the frontier." Having noted his local interest and previously asserted that the Romans maintained the area north of Kippen as a marsh to protect themselves from the Picts, Begg further states: "One of the reasons for the survival of the British kingdom can only have been the security afforded by the impenetrability of its northern frontier. If the sequence of events in the upper Forth Valley was as suggested above, the Britons inherited from the Romans a shield that gave their kingdom a vital degree of effective protection from its potentially extremely dangerous northern neighbours. Indeed, intriguingly, we are told that about 970, Kenneth II, King of Scots [Alba], enraged by the independence of Strathclyde, launched a punitive assault on the Britons which failed because 'his army came to grief when it was caught on boggy ground.'". Begg also notes the view of O.G.S. Crawford that the Fords of Frew was a gateway between Strathclyde and Alba, quoting Crawford thus: "the passage of the Fords of Frew was primarily a route leading form Dumbarton, the old British stronghold, into northern Scotland by Strathallan and Strathmore".
When in 1018, King Malcolm II of Alba met Uchtred, Earl of Northumbria, in the Battle of Carham, the Scots troops had already proved themselves by defeating a Danish invasion at Mortlach in 1010. Aided by King Eoghain the Bald of Strathclyde who died in the battle, the Scots were victorious. News of this defeat reached King Canute who summoned the Northumbrian Earl to his court and had him assassinated. Uchtred was succeeded in the earldom by his brother Eadulf who promptly ceded to King Malcolm II the lands of Lothian in return for peace. By this time the lands would have already been in Malcolm's possession.
The heir of Eoghain the Bald to the throne of Strathclyde was Malcolm's own grandson, Duncan. He was to be the last King of Strathclyde, for on the death of King Malcolm II of Alba in 1034, he also succeeded to that throne, thus joining the two kingdoms as one; Scotland.