Before the Scots came in the 6th century, the land they were to occupy was Pictland, inhabited by many diverse tribes known to us collectively as the Picts. When Kenneth MacAlpin united Dalriada with Pictland, he called the combined country Alba. That was the name it still had in Macbeth's day, although its inhabitants were called Scots. By tradition, Scotland had seven provinces, called Mortuatha (great tribes): Caithness, Moray, Ce, Cirech, Atholl, Fortriu, and Fife. This was the height of the Viking era. Norse chieftains held not only Norway and Iceland, but the Orkney Islands just north of Scotland and the tiny Shetland Islands between Scotland and Norway. They also held, at various times, parts of northern Scotland, the Western Isles (Mull, Skye, etc.), and large parts of Ireland. Leif Erikson, reputed to have landed in North America before Columbus, was a contemporary of Macbeth's father.
In Dalriada, the first nation of Scots established in present-day Scotland, the two ruling houses were the House of Gabhran and the House of Loarn. Kenneth mac Alpin (843 AD) was of the House of Gabhran, and when he united Pictland and Dalriada into the single kingdom of Alba, he shut out the House of Loarn from succession, alternating the kingship instead with his brother Aed's house. This went on until for nearly 200 years, until Malcolm II decided to keep the kingship for his own heir, Duncan apparently, by killing all the eligible claimants from the alternate house--including an unnamed son or grandson of Boite, who was either brother or nephew to Macbeth's wife, Gruoch.
The kingdom of Alba which Máel Coluim ruled had been created over the previous century and a half, largely by the efforts of three kings, Causantín mac Áeda (900–943), Cináed mac Maíl Coluim (971–995) and Máel Coluim mac Cináeda (1005–1034), who had ruled the kingdom for almost a century. By this time, one competing segment of the royal lineage, that of Causantín mac Áeda, appears to have been wiped out and a second segment, descended from Dub, brother of Cináed mac Maíl Coluim, appears to have given the struggle for the throne and accepted the Mormaerdom of Fife in compensation.
Born in 1001, Duncan was the son of Crinan, Abbot of Dunkeld and ruler of Atholl, and Bethoc, daughter of Malcolm II. Duncan, King of Scots, a grandson of Malcolm II, Duncan was made king of the client kingdom of Cumbria in 1018 and succeed Malcolm as ruler of Alba in 1034. His two sons, Malcolm Canmore and Donald Ban (Donalbane), later became kings in Alba, as well.
Another Norse people, with close cultural and linguistic ties to the Northmen, the Danes were a powerful force and held large portions of western England during the early part of the 11th century. Cnut was king of Denmark, Norway and England from 1016 to 1035. The annals record that in 1033 the son/grandson of Boite was killed by Malcolm. At any rate, his outraged relatives--kin to Macbeth's wife--rose up against Malcolm II. They were defeated in battle, but Malcolm received his death wound and perished at Glamis in 1034. As the designated choice of a strong and apparently popular king, Duncan became the ruler in Alba. But shortly thereafter, he led an ill-fated attempt to take the city of Durham in Northumbria, some distance across the English border. In a strategic blunder, he sent his cavalry in first against the walled city; they were devastated by the Northumbrian archers, and when next Duncan's foot soldiers charged the walls, the Northumbrian cavalry rushed out from the city and cut them down. 3000 Scots died. The Northumbrian women gathered their heads, washed them and braided their hair, and they were put on pikes around the city walls.
Malcolm II may have used a marriage alliance to gain nominal claim to the province of Caithness, previously a Scottish holding. Thorfinn was his grandson and had the proper lineage to claim the high kingship. And if we also accept that Macbeth's mother was another daughter of Malcolm II, then Thorfinn and Macbeth were first cousins. Thofinn's mother was the daughter of Malcolm of Moray, it would have been one in a long line of marriages between the northern Scots and the Norse on their border. It might also explain the relative peace between Caithness and Moray after the battle of Skitten Myre. The Norse sagas credit Thorfinn the Great with rampaging through Scotland and being proclaimed king.
The Book of Kells, source of much history from this time period (of Dalriada), refers to the ruler of Moray and the high king of Alba with the same term: King of Scots and the two ruling houses were the House of Gabhran and the House of Loarn. Moray was a constant thorn in the side of the Alban high kings, and many battles are recorded between the high king's forces and the men of Moray. In 1040, the righ and foremost warlord of the House of Loarn was Macbeth.
Even when Edward the Confessor returned from exile to take the English throne in 1037, many of the earls who served him were Danish. There was contention between Denmark and Norway, however, both before and after Cnut's supposedly united reign, and there were numerous times when the Norse in Ireland tramped across southern Scotland to attack the Danes in York, and vice versa. In the 11th century, there was still a struggle between the Celtic church and the Roman church. Though the Scottish Primate (the Bishop of St. Andrews) officially looked to Rome, the monks and priests working among the people came out of the Celtic tradition, and many of its practices--such as clergy taking wives--were still pervasive in Scotland. At this point in time, the Irish were just battling their way out from under Norse rule. The infamous king Brian Boru won his many battles just prior to the 11th century. They were a Celtic people with cultural and marriage ties to the Scots, and a common language.
Macbeth was born in 1005, his father was Findlaech mac Ruadri, mormar of Moray and his grandfather was Ruadhri (pronounced Roary). Moray was in the grip of a virtual civil war between those loyal to one or other branch of the Cené lLoairn. Findlaech owed allegiance to Malcolm II of Alba, due to Malcolm's intervention in a disastrous campaign to wrest the province of Caithness back from the Norse in about 1007 (the date is unclear); hence the title of mormaer, which means "steward."
But who was his mother? Several centuries after his death, an account appeared that said Macbeth's mother was a daughter of Malcolm II, and such would not be illogical--a marriage alliance to insure Findlaech's loyalty fits the pattern of Malcolm II's diplomacy, which included marrying one of his daughters to the leader of Atholl and, possibly, another to the Viking ruler of Caithness and Orkney, Sigurd II Hlodvirsson of Orkeny. In 1020, Findlaech was challenged for rule of Moray by his two nephews, Malcolm and Gillacomgain mac Maelbrigte, and killed. These two succeeded to the mormaership in turn. Macbeth sought refuge at the court of his grandfather, Malcolm II. In 1029, Malcolm of Moray died in a riding accident and was succeeded as mormaer by his brother Gillecomgain. Gillecomgain married Gruoch and they had a son, Lulach, born in 1031. The annals report that Gillecomgain died in a fire with 50 of his men.