From ‘The Grand Chessboard’ (1997) by Zbigniew Brzezinski,

The overseas British Empuire was initially acquired through a combination of exploration, trade, and conquest. But much like its Roman and Chinese predecessors or its French and Spanish rivals, it also derived a great deal of its staying power from the perception of British cultural superiority.

‘Cultural superiority’ as the key to the staying power of an empire is the main theme in the book so far