On Wednesday, King Salman of Saudi Arabia pushed aside his heir-apparent, Crown Prince Mohamed bin Nayef, and moved his own son Mohamed bin Salman into that spot. He also removed Mohamed bin Nayef (known as MbN) from his powerful post as interior minister, meaning that MbN’s days in the sun are entirely over.

What’s up? Why did this happen, and what comes next?

Here are a few key points.

First, it has been obvious since King Salman ascended to the throne in January 2015 that he wanted his son Mohamed bin Salman (known as MbS) to succeed him. The young man was the apple of his eye, and was immediately named deputy crown prince. The question was whether the aged king — now 81 and in questionable health — would live long enough to elevate young MbS, who was then only 29 and is now 31. The danger, for the king, has been that he would die suddenly, and that MbN would ascend to the throne and remove his cousin MbS from the line of succession. This week the king decided that waiting is not smart: Why take chances? Perhaps there is a saying in Arabic that resembles “God helps those who help themselves.”

Second, we now know (barring calamities like assassination) who will rule the kingdom for many decades. King Salman may rule for several additional years, but there is no reason MbS cannot rule after him for 50 more. This has never happened before. The Saudi system has had brother succeed brother — all of them the sons of the founder of the modern kingdom, Ibn Saud (1875–1953). Naturally, as his sons succeeded each other more or less in order of age, each successor was older than his predecessor; as noted, Salman was 79 when he became king. So the system has produced geriatric rule for decades now, while the Saudi population grew younger and younger. The CIA World Factbook says the median age in the kingdom is now just 27. And now the kingdom will have a ruler from those younger generations — for the first time ever.

Third, the Saudi system of brother following brother could only work for one generation — and King Salman was the end of that system. Ibn Saud had 45 sons of whom 36 survived to adulthood, and some of them were clearly ineligible to be king. So, there were a limited number of truly eligible brothers to take the throne from his death in 1953 until now — seven decades. But all those sons of the founder simply had too many sons themselves, and there has been no workable principle for figuring out how to choose a king in the follow-on generation. It looked like the first person in that generation, the grandchildren of the founder, would be MbN, but that’s over; it will be MbS. And (again, barring some calamity) he will rule for decades. What may happen by the time the aged MbS leaves the throne in, say, 2070, is that his line will have seized and will thenceforth keep the throne. He might name a son of his as crown prince, and that son could serve for ten or 20 years and be accepted as successor, and the old Saudi system will have changed: The bin Salman line will be the true royal family, and the others will all be on the outs.

Why should they accept that outcome? Because no one has offered an alternative that’s better, and there does have to be a king; Saudi Arabia is a monarchy. If there is an election of sorts for king, among thousands of princes who are both voters and candidates, that’s close enough to an electoral democracy to give non-royal Saudis modern ideas about actual elections — something the royals will want to discourage — and would diminish the status of whoever was “elected” king. Moreover, there are still plenty of jobs and financial rewards to pass around. Mohamed bin Nayef’s father, Prince Nayef, was minister of the interior and MbN got the post when his father died. In this week’s shake-up MbN was removed not only as crown prince but also as minister of the interior; but a nephew of his, Abdul Aziz Bin Saud Bin Nayef, age 33, was given the post — keeping it in the bin Nayef line and thereby reducing intra-family dissension. A son of Prince Bandar bin Sultan, the long-time ambassador to Washington, was named ambassador to Germany, so the bin Sultans (Prince Sultan, Bandar’s father, was the minister of defense from 1963 until his death in 2011) also get a prize.

Whether the bin Salmans can keep the line of succession is a question that will engage the entire royal family, but presumably need not be faced for decades. Meanwhile, Saudi Arabia is about the only country on earth whose likely ruler for the next half-century can now be identified. And that man, MbS, has plenty to worry about. The Saudi population is now over 30 million and, as noted, skews young, but is ill-trained for modern jobs. Forbes reported last December that “Unemployment in Saudi Arabia rose to 12.1% in the third quarter of the year, marking a four-year high. And although the labour force participation rate of Saudis rose to a record level of 42%, most jobs that are being created are going to expatriates.” Oil revenues have of course sunk as oil prices declined by half in the last few years, and the kingdom runs a budget deficit; it was $79 billion last year. Saudi reserves, once over $730 billion, have now sunk to under $500 billion and are still falling. MbS has a plan to deal with all of this, called Saudi Vision 2030, and the goal is right: Move from an oil-only economy into a more normal and diversified one, meanwhile loosening some of the strictures (on women, for example) that have held the kingdom back.

Right goals, but who can say if he will succeed? And meanwhile, MbS must help his elderly father cope with Iranian expansionism, war in Syria and Yemen, Islamist and jihadi challenges, and a long list of other worries. Uneasy lies the head that will now, clearly and for a very long time, wear the crown.

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— Elliott Abrams is a senior fellow for Middle Eastern Studies at the Council on Foreign Relations and a former Deputy National Security Advisor. His new book, Realism and Democracy: American Foreign Policy After the Arab Spring, will be published in September by Cambridge University Press.