The latter part of King Nechtan`s reign was marked by a long and bitter struggle for power between the King`s three rivals. The first signs of trouble began in 713 and did not end until the victory of King Oengus 1 over his rival Drest in 729
Although loosely based around geographical features and given cohesion by tribalism, a kingdom was essentially one man`s possession and it`s fortunes rose and fell with him. From the eighth century onwards the ruling families of Pictland became increasingly dominated by the Scots and in the ninth century a series of Dalriadic Kings ruled simultaneously over Dalriada and Pictland. Thus when Kenneth mac Alpin of Dalriada assumed the leadership of the Picts about 843, for all political purposes the Pictish Kingdom ceased to exist.
Oengus 1, was the last of the great Pictish Kings. Indeed, since he may well have been part Scottish, the Dalriadic take over of Pictland was probably already under way by the time of his reign. Once he had made sure of his position at home, he renewed his pact of friendship with the Northumbrians and turned his attention to Dalriada in the west. Fighting first broke out in 731 when Oengus`s son Brude, mad a successful sortie into Dalriada. The seizure of Brude while in sanctuary two years later gave Oengus the excuse he needed to take advantage of Dalriada`s internal divisions and launch a massive strike right at the heart of Scottish territory. The Picts managed to break through to the west coast thereby dividing the Kingdom and putting themselves in an excellent position from which to organise an even more devastating campaign in 736. The great stronghold of Dunadd was taken and a large area of the country pillaged. After further expeditions in 741 Dalriada was brought completely under Oengus`s control.
There are indications before this that the Northumbrians were not happy with their success, for in 740 King Eadberht of Northumbria had broken his peace with the Picts and engaged in some indecisive cross-border raiding.
Oengus declared overlord of Dalriada in 741. What appears to have been a gradual merger through inter-marriage of the Scottish and Pictish ruling families. The ruling classes were more of Celtic stock.
However, it was not from the Northumbrians that Oengus met his `come uppance,` but from the powerful British of Strathclyde. The survival of Strathclyde over the other two and a half centuries was no mere historical accident. The close knit nation played a significant part in the internal dealings with Pictish war bands, as Oengus found to his cost in 750. In that year an army led by his brother Talorgen was soundly defeated in Strathclyde and Talorgen killed. Oengus`s response was to reform his alliance with King Eadberht of Northumbria and organise a joint raid on Strathclyde at the capitol Dumbarton in 756. He had chosen a fortress too far, and after some initial successes the raiders forces were destroyed. Oengus had fought his final battle. Managing somehow to escape the slaughter, he made his way back to the east where he lived for a further five years. The rash southern adventure had shattered the myth of his invincibility, and although he retained control over Dalriada until his death, Pictish power was probably already on the wane. There is a possibility that had he not over stretched himself by challenging the British of Strathclyde his remarkable achievements up to that point could have endured. Had they done so, the northern part of Britain might still now be named Pictland .
About 717 Nechtan ordered all Columban monks in Pictland to return to Iona, though by this time the island community itself had moved to Rome, and for a while the Picts and the Northumbrians seemed to have lived at peace with each other. Nevertheless
Nechtan`s career did not become any easier, and in spite of the accord with the Picts he finally lost his throne to Oengus in 729
We will probably never know precisely how Kenneth macAlpin became king of the united Scotland and the Pictish kingdom in the middle of the ninth century. After the death of King Oengus 1 of the Picts in 761, the sources become particularly confusing. Those from Iona stop about 740, and usually reliable supply of Northumbrian information dries up in the ninth century, when Vikings took over the north east of England. At the time of his death King Oengus, the Pictish King was almost certainly in control of Dalriada. He may have been part Scot as his name is Gaelic. His forays and attempts to the west may have been to win a throne to which he felt he had a reasonable claim. His successor being his brother Bridei, followed by King Kenneth who in 768 was defeated by Aed Fund of Dalriada c. 758 – 778 in Fortriu.
The Rise of Oengus, son of Fergus.
Oengus, son of Fergus was the Picts greatest military leader, (the Irish form of his name reads—Onuist, son of Uurgist. Had his successors been able to consolidate his achievements, the modern Britain would certainly have been named by Picts, rather than the Scots. Oengus won his way to the throne of Pictland in a dramatic succession of victories over a period of time of two years, which held the interest of Irish annalists. He showed himself far and away the ablest of four contestants for the throne, and after he was firmly established there he turned his energies to the conquest of neighbouring kingdoms. The first sign of civil discord in Nechtan`s reign comes as early as 713, when Irish Annals report that his brother Cinoid had been murdered by the king of the district of Atholl. Nechtan reacted immediately by imprisoning the murderer, and this prompt reprisal seems to have put a stop to any trouble for about ten years. In 724 Nechtan voluntarily retired. According to the Annals entered a monastery, allowing Drust to succeed him. The following year the son of a new Pictish King was imprisoned and the year after Nechtan himself was captured, indicating that he was being pressed from the start. Drust`s kingship was short lived for in 726 he was `cast from the Kingdom of the Picts and Alpin reigned in his place`.
The contestants in what can be called the `Pictish wars of succession ` were Nechtan, who had a long reign behind him, Drust who had challenged Nechtan`s position, Alpin who had opposed Drust, but of whom little was known and lastly Oengus, the ultimate victor, whose origins are equally obscure. They were all Picts for the battles in which they engaged were described by the Irish Annalists as having `taken place between the Picts themselves. They were possibly all leaders of various districts in Pictland, who could muster their followers. Four battles were fought before the Kingship could be established, between 728 and the 12th August 729. Moncrieff Hill reckoned where the first battle was fought, a place south of Perth. Many `men of Alpin ` were slaughtered, however, Oengus left Nechtan to slay Alpin.. This allowed Nechtan for a brief period to assume the title King of the Picts. In 729 a battle encounter between Nechtan and Oengus ended now King of the Picts. The final contest called Cath Droma Deirg Blathug and the death of Drust firmly established Oengus`s place on the throne.