Saudi Arabia is transforming. Long characterized by a slow and steady approach to policy making, the pace of change has accelerated beyond recognition. When King Salman replaced Crown Prince Muqrin in 2015 it was unprecedented, but he’s now repeated the move barely two years later to raise his son Prince Muhammad bin Salman to the position of heir on 21 June.

Muhammad bin Salman had increasingly been the dominant driver of Saudi policy over the past 18 months from his position of...