Lowlanders, Celts & Beginnings of the Troubles

From The Road to Guilford Courthouse, by John Buchanan, ©1997, John Wiley & Sons, pp. 120-121:

There are Celtic myth enthusiasts who believe the Scotch Irish were Celts, have peopled with Highlanders whole American landscapes where there were none, imagined bagpipes on American battlefields that never echoed their wails, conjured a Celtic culture for an entire American region where it never existed. But the Scotch Irish were not Celts by either blood or culture. Their ancestors were Lowland Scots, inhabitants of a poor, backward, violent land. The difference between the Lowland Scots and the more famous Highland Scots should be established immediately. All that Lowlanders and Highlanders had in common, besides wretched poverty, was a political line on the map separating Scotland and England, and their incompatibility survived the Act of Union (1707) of the two kingdoms well into the nineteenth century. They might have lived in very different countries, for they were very dissimilar people and they hated each other.
The hardening split between Highlanders and Lowlanders had developed at least by the late fourteenth century and was rendered more intransigent by deep ethnic and cultural differences. ... To these differences was added after the Protestant Reformation the profound distinction between Protestant Lowlanders and largely Catholic Highlanders in an age of fierce religious conflicts.
In the early seventeenth century, in a continuation of an effort England had begun five centuries before to subdue Ireland, James I of England, who was also James VI of Scotland, confiscated the Ulster lands of the Irish aristocracy and created the Plantation of Ulster. On it were settled Scottish Lowlanders and English farmers and Londoners, Protestants all. Earlier settlements under private initiative were also composed of Scottish and English Protestants. James also hoped that flooding the land with Lowland Scots and English would prevent joint actions by Irish Celts and Scottish Highland Celts. Thus were the seeds planted for the terrible "troubles" we have witnessed on our television sets for the past decades.

The Scots-Irish

Scots-Irish is an ethnic group from Ireland which ultimately traces its roots back to settlers from Scotland, and to a lesser extent, England. In particular Scots-Irish can often be traced back to the Scottish Highlands, Scottish Lowlands, Galloway, and the Scottish Borders.
The Scots-Irish and their descendants are primarily found in Ulster, where they are Ulster Scots, and in Canada and the USA, laterly where they are often identified as Scotch-Irish. Most Scots in Ireland are Ulster Scots, although there are also some who live in the Republic of Ireland, mainly in Donegal.
The Scots-Irish are strongly identified with Protestantism and, in modern day Ireland, unionism.
The Ulster-Scots are predominantly Presbyterian, with many Anglicans, some Congregationalists, and some Quakers. In America, many Scots-Irish people gravitated towards the Methodist and Baptist denominations. In Ireland, Ulster Scots are usually identified with the Irish unionist tradition, although many Ulster-Scots involved themselves in the Society of United Irishmen, an Irish republican organisation in the late 1790s.

(Source: Wikipedia)