History of Scotland: Picts, Scots, Britons, Angles, Norsemen
Before the withdrawal of the Roman legions from Britain, Scots from Ireland were establishing their power in what is now Argyll. Soon afterward the Angles began to occupy Lothian, and the Britons who had lived under Roman rule were driven westward. Thus, by about 600 A.D. four peoples were living on the Scottish mainland.
The Picts occupied most of the Highlands, except for the Scots colony in Dalriada (Argyll), while the western Lowlands (Strathclyde) were held by partially Romanized Britons and the southeastern Lowlands (Lothian) by the Angles. For a time it seemed likely that the Angles would extend their sway to the north and west, but their progress was decisively checked by the Picts at the Battle of Ntlchtansmere (685).
The Norse raids and invasions added a fresh element to the population and it was largely owing to the needs of defense that Kenneth MacAlpin (Kenneth I) secured recognition as ruler of a united Pict-Scot kingdom, sometimes called Alban (about 843). Not until after the Battle of Carham (1016 or 1018) was Lothian finally added to Alban. In 1034, Strathclyde, after a long period as a satellite state, was also incorporated in a united kingdom of Scotland, which did not at first include the islands or the northernmost mainland counties. Caithness and Sutherland were recovered from the Norsemen by William the Lion (William I, reigned 1165-1214), though royal authority there was merely nominal until the reign of James IV. After the Battle of Carham (1016 or 1018) was Lothian Hebrides and the Isle of Man (1266). But here, too, until the reign of James IV, the lords of the Isles were more often in practice independent sovereigns than Scottish vassals. Orkney and Shetland were pledged to Scotland by Christian I of Denmark in 1468-1469 as part of his daughter's dowry on her marriage to James III and since then have been part of the Scottish kingdom. Geographic, but not political, unity was thus established.