Scotland during the Medieval and Renaissance periods was divided, both physically and culturally, into two sections: the Highlands and the Lowlands. Highlanders descended almost exclusively from the Celtic tribe -as the Picts, and fiercely retained their Celtic ancestral traditions. The mountainous Highlands to the northwest remained primitive and uninfluenced by the cultural and scientific advances which made up the "Renaissance". Highlanders tended to adhere to the clan system of self-rule. The Highlanders had resisted the Romans and all the succeeding invaders who had attempted to subjugate them, and they occasionally launched raids against the English. In the process, the Lowlands region, lying between the two opponents, was invariably overrun by them. (Caithness Lowland Scots) and Shetlandic, is essentially a form of Scots.
The people of the Lowlands, on the other hand, descended from an intermingling of at least nine different races: the aboriginal natives, the Gaels, the Britons, the Romans, the Teutonic Angles, the Saxons, the Normans, the Flemish, and the Scots. The last named group, the Scots, were a Celtic tribe which originated in Ireland and had, during the Third and Fourth Centuries AD, invaded and established colonies in (Alba) Scotland, around the Twelfth Century, to the concept of feudalism.
When Shakespeare wrote his play, he was dependent upon the only sources available to him - Raphael Hollinshed's Chronicle of Scotland (1580s) and John Bellenden's translation of Hector Boerce's History and Chronicles of Scotland (1536). A work now regarded as largely fiction. It was Boece who invented the character of 'Lady Macbeth', refined by Shakespeare into his 'fiend-like queen'. Macbeth's historical wife was Gruoch, who was either a niece of Malcolm II or a granddaughter of Kenneth III. As for which, her father was 'Boite, son of Kenneth' whose grandson was killed by Malcolm II in 1033 by no record of which Kenneth was Boite's father. Gruoch was born of a royal line at odds with Malcolm and presumably the house of Dunkeld, where he had designated his succession. But she also had reason for hostility towards Macbeth, since she had earlier been the wife of Gillacomgain MacRuari, burned to death by Macbeth or his followers. The marriage took place before Macbeth's succession and was most likely a political union, designed to bring peace between the contending kindreds of Moray. Shakespeare tells us MacBeth's home was in Ross, although it bordered Norse-held Caithness and may have answered to Thorfinn instead of the House of Loarn that once shared the High Kingship with the House of Gabhran.
Shakespeare wrote the play 'Macbeth' in 1606 - three years after the union of the Crowns of Scotland and England under James VI and I, of the Scottish Stuart family. Shakespeare put a confluence on Holinshead's version in the "Chronicles" (published in 1578), making Macbeth the villian in order to flatter the new King. In the play, Macbeth murders Banquo, the legendary founder of the house of Stewart, but Banquo's son Fleance survives him. Thus, Fleance of the line of Stewart is the rightful heir to the throne of Scotland, but the throne has been usurped by the murderer, Macbeth. Of course, all of this is intended for the contemporary audience of 1606. After the murder, Macbeth visits the three witches in their cave, symbolised by a triple sceptre representing the combined crowns of Scotland, England and Ireland- the Mormaer is the last of his line, shown by a vision of the descendents of Banquo ruling over a mighty realm. In addition, James was obsessed with the occult in general and witches in particular. Shakespeare lists them as the 'three witches' in his dramatis personae. They don't have an understandable equivalent in Celtic tradition, and are more characteristic of Norse prophetic women. Before then, it retained the meaning of the Anglo-Saxon 'wyrd', meaning fate or destiny. The three 'wierd sisters' were most likely intended to reflect the Norse tradition of the three Norns, or women (Wyrd, Verdandi and Skuld) who sit beside the well which springs from the roots of the Yggdrasil (World Ash Tree), spinning out the destiny of mankind. Macbeth became influenced by his hereditary enemies, the Orkney jarls.