More than 27 million Americans today can trace their lineage to the Scots, whose bloodline was stained by centuries of continuous warfare along the border between England and Scotland, and later in the bitter settlements of England's Ulster Plantation in Northern Ireland. Between 250,000 and 400,000 Scots-Irish migrated to America in the eighteenth century, traveling in groups of families and bringing with them not only long experience as rebels and outcasts but also unparalleled skills as frontiersmen and guerrilla fighters. Their cultural identity reflected acute individualism, dislike of...