Four years ago this month, Prince Salman bin Abdul-Aziz Al Saud ascended to the throne of the Kingdom of Saudi Arabia. His reign has changed the kingdom profoundly: It is more repressive than ever, more unpredictable than ever and likely less stable than at any time in a half century. The kingdom is in the midst of important and challenging transformations.

Salman was governor of Riyadh province for a half century before his half-brother, King Abdullah, made him crown prince. As the chief of the capital, Salman oversaw its transformation from a remote desert town to a modern city and the centerpiece of the country. He did so with the careful cultivation of the Wahhabi clerical establishment. He also was the policeman of the royal family, most of whose members lived in his jurisdiction.

For a half century before his ascension to the throne the line of succession in the kingdom was predictable and clear: The sons of Ibn Saud would inherit the throne as they aged. The question of succession is the Achilles heel of absolute monarchies.

Salman has twice changed the line of succession without any explanation. Two crown princes have been dismissed to open the door for the king’s son, Prince Mohammed bin Salman. Former Crown Prince Mohammed bin Nayef is under house arrest, quarantined from his own family. Apparently the king and crown prince regard Mohammed bin Nayef as a potential rival for the loyalty of the royal family.