With the succession to King Abdulaziz having passed among his many sons since his death in 1953, a key question for many Saudi-watchers, particularly those outside the kingdom, was how the royal family would manage the generational transition that had to happen sooner or later. On his first day as king, Salman settled the issue by nominating his nephew, Mohammed bin Nayef, deputy crown prince, signalling, for the first time, a pathway to the grandsons of Abdulaziz. Three months later, in April 2015, Salman removed the existing crown prince, his youngest surviving half brother Muqrin, replaced him with Mohammed bin Nayef, and brought MBS into the line of succession as the new deputy crown prince.
With these acts, which were unprecedented in the modern history of Saudi Arabia, Salman set two precedents; first, that his successor would come from the next generation of royals, and, second, that an incoming king could alter the line of succession that he inherited from his predecessor. Salman's predecessor, King Abdullah, also cycled through two crown princes, but he outlived them both and did not remove them as Salman has done.
A potential area of concern both for MBS and for the king may have been that Mohammed bin Nayef might have been tempted to follow Salman's practice and amend the crown prince when he took the throne. In such reasoning, the only way to ensure that MBS followed his father as king would have been to create a direct line of succession that bypassed Mohammed bin Nayef.
The upper echelons of the Al Saud are, famously, a black box closed to outsiders, and we may never know the precise reasons (or timing) for the removal of Mohammed bin Nayef and appointment of MBS. It may indeed be the case that Mohammed bin Nayef's health was failing. He has reportedly suffered from the after-effects of an assassination attempt in 2009 when a member of al-Qaeda in the Arabian Peninsula blew himself up just metres away.
It certainly is the case that over the past two years there has been a steady concentration of power and responsibility around MBS, and that a string of appointments made in April - including that of his 28-year-old brother Khalid as Saudi ambassador to the United States - were perceived by many as consolidating MBS's position across the diplomatic, economic, security, defence and intelligence spectrum. With Saudi Arabia facing a volatile regional situation and beginning the array of economic overhauls associated with MBS's Vision 2030 economic retooling, there may simply have been an appreciation of the need for decisive, long-term leadership.
How this plays out within the Al Saud and among Saudi Arabia's regional and international partners will be important. Two anonymous letters written in September 2015 appeared to indicate a level of disquiet among at least a section of senior royal family members toward MBS - the announcement that MBS's appointment as crown prince by 31 of the 34 members of the Allegiance Council may have been intended, in part, to portray a united front against any recurrent acts of dissent. Within the Gulf Co-operation Council - the hawkish axis that binds Saudi Arabia and the Abu Dhabi emirate through MBS and Mohammed bin Zayed - will likely strengthen still further, but may, in the process, intensify the centrifugal pressures that are weakening the GCC among the three states - Kuwait, Oman and Qatar - that do not share the hard-line approach to regional security.
Internationally, the rise of MBS to crown prince - and possibly king sooner rather than later - may be viewed with a degree of ambivalence in Western capitals, including Washington. Many in the security and counterterrorism establishment in Washington had forged productive working relationships with Mohammed bin Nayef that smoothed relations strained by 9/11, and scrambled to get the measure of MBS after 2015 (similarly, the lengthy interviews MBS gave to western media, including the Economist, Bloomberg, and, most recently, the Washington Post, may have been designed to sell the prince to a western audience).
Finally, the close ties that are said to have developed between MBS and US President Donald Trump's son-in-law and adviser Jared Kushner could be instrumental in packaging the "new" Saudi Arabia under a similarly ambitious political neophyte dismissive of tradition and willing to think outside of the box as a cornerstone of the Administration's approach to the Middle East, for good or ill.