Peerage
Country the peerage was created in.  All Dukes first created by the King of England come before those created by the King of Scotland.  After this come Dukes of Great Britain whose titles were created between 1707 and 1801 (during the existence of the United Kingdom of Great Britain). In 1801, the kingdom of Ireland joined with Great Britain to form the United Kingdom of Great Britain and Ireland, so Dukes of Ireland come next, followed by Dukes of the United Kingdom. The other types of peer follow in the same order.