In 2014 I wrote a book, “The Saudi Kingdom,” that was, frankly, pessimistic about Saudi Arabia’s long-term prospects. After decades under a geriatric leadership class that had done too little for too long, I concluded with a blunt prescription: the Kingdom needed a strong reformist leader—someone willing to restructure the entire system, society, and economy.

In January 2015, King Salman Bin Abdulaziz Al Saud acceded to the throne and promptly empowered his son, Prince Mohammed bin Salman (MBS), to launch a far-reaching program of reform. This August, MBS turned 40—having completed a decade in power since taking on core portfolios in 2015—and the Saudi Arabia of today is almost unrecognizable from the country I wrote about a mere 11 years ago.

To understand the distance traveled, it he

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