If we're recommending books on Scottish History can I add that the best book I have ever read about that turning point in Scottish History - the Scottish Enlightenment post the 1707 Union of Parliaments - was written by an American academic, Arthur Herman: "The Scottish Enlightenment - The Scots' Invention of the Modern World" (ISBN 1-84115-276-5).

Among many other things he deals with the formation of presbyterian Northern Ireland and the spread of Scots to other parts of the world, especially the USA. A lively and fascinating read.