A Bronze Age empire stagnated for much the same reason that a nationalized industry stagnates: monopoly rewards caution and discourages experiment, the income is gradually captured by the interests of the producers at the expense of the interests of the consumers, and so on. The list of innovations achieved by the pharaohs is as thin as the list of innovations achieved by British Rail or the US Postal Service.

Matt Ridley, The Rational Optimist.