Attention: Saudi Prince in a Hurry-Thomas L. Friedman

To understand the upheaval that is taking place in Saudi Arabia today, you have to start with the most important political fact about that country: The dominant shaping political force there for the past four decades has not been Islamism, fundamentalism, liberalism, capitalism or ISISism.

It has been Alzheimer’s.

The country’s current king is 81 years old. He replaced a king who died at 90, who replaced a king who died at 84. It’s not that none of them introduced reforms. It’s that at a time when the world has been experiencing so much high-speed change in technology, education and globalization, these successive Saudi monarchs thought that reforming their country at 10 miles an hour was fast enough — and high oil prices covered for that slow pace.

It doesn’t work anymore. Some 70 percent of Saudi Arabia is under age 30, and roughly 25 percent of them are unemployed. In addition, 200,000 more are studying abroad, and about 35,000 of them — men and women – are coming home every year with degrees, looking for meaningful work, not to mention something fun to do other than going to the mosque or the mall. The system desperately needs to create more jobs outside the oil sector, where Saudi income is no longer what it once was, and the government can’t keep eating its savings to buy stability.

That’s the backdrop for this week’s daring, but reckless, power play by the 32-year-old son of King Salman — Crown Prince Mohammed bin Salman, known by his initials M.B.S. I’ve interviewed M.B.S. twice. He is a young man in a hurry. I’ve found his passion for reform authentic, his support from the youth in his country significant and his case for making radical change in Saudi Arabia compelling.

Indeed, there are two things I can say for sure about him: He is much more McKinsey than Wahhabi — much more a numbers cruncher than a Quran thumper. And if he did not exist, the Saudi system would have had to invent him. Somebody had to shake up the place.

But here is what I don’t know for sure: Where does his impulse for rapid reform stop and his autocratic impulse to seize all power begin? After M.B.S. arrested a slew of Saudi princes, media owners and billionaire businessmen on “corruption” charges, President Trump tweeted his applause, saying, “Some of those they are harshly treating have been ‘milking’ their country for years!”

I could only laugh reading that tweet. Hearing that Saudi princes were arrested for “corruption” is like reading that Donald Trump fired seven cabinet secretaries “for lying.” You know it has to be something else. Trump obviously missed the story last year that M.B.S. impulsively bought a yacht while on vacation in the south of France — it just caught his fancy in the harbor — from its Russian owner for $550 million. Did that money come out of his piggy bank? Savings from his Riyadh lemonade stand? From his Saudi government 401(k)?

I raise this point because when you’re making as many radical changes at once, and making as many enemies at once, as M.B.S. is, your robes need to be very clean. People have to believe that you mean what you say and that you have no hidden agendas, because change is going to be painful. Look at what M.B.S. is doing all at once:

To speed up decision-making, he is reshaping the Saudi state — from a broad family coalition where power is shared and alternated among seven major families and decisions taken by consensus — to a state governed by a single family line. This is no longer “Saudi Arabia.” It is becoming “Salman Arabia.” In the latest series of arrests, M.B.S. basically eliminated the “young old guard” — the key sons and his natural rivals from the other main Saudi royal lines. He also arrested the owners of the three main quasi-independent private television networks, MBC, ART and Rotana.

At the same time, M.B.S. is shifting the basis of legitimacy of the regime, ending “the 1979 era.” In 1979, in the wake of the takeover of Islam’s most holy site in Mecca by an ultra-fundamentalist Saudi preacher who claimed that the al-Saud family was not Islamic enough, the Saudi ruling family — to shore up its religious legitimacy — made a sharp religious turn at home and began exporting its puritanical Wahhabi Sunni Islam abroad, building mosques and schools from London to Indonesia.

It has been a disaster for the Arab/Muslim world, spawning offshoots like Al Qaeda and ISIS and retarding Arab education and women’s advancement.

M.B.S. has vowed to give birth to a more moderate Saudi Islam, starting by curbing his religious police and permitting women to drive. This is hugely important. He is daring people to judge his government not on piety but on performance, not on Quran but on KPIs — key performance indicators on unemployment, economic growth, housing and health care.

But he is replacing Wahhabism as a source of solidarity with a more secular Saudi nationalism, one that has a strong anti-Iran/Persian/Shiite tenor. And that is taking him to some dangerous places. To confront Iran, M.B.S. got the Sunni Prime Minister of Lebanon, Saad al-Hariri, to quit his office on Saturday while on a visit to Riyadh, and blamed Iran and its Shiite allies for making Lebanon ungovernable — and for a missile attack from Yemen. Lebanon, which had forged a relatively stable balance among Sunnis, Christians and Shiites, is now shaking. M.B.S. also led a Gulf effort to isolate Qatar for being too close to Iran and to crush Iran’s influence in Yemen — and crush Yemen in the process. It’s overreach, and there seems to be no one around to tell him that.

As a veteran Saudi journalist remarked to me of M.B.S.: “This guy saved Saudi Arabia from a slow death, but he needs to broaden his base. It is good that he is freeing the house of Saud of the influence of the clergy, but he is also not allowing any second opinion of his political and economic decisions.”

I worry that those urging M.B.S. to be more aggressive in confronting Iran (whose malign regional influence does need counterbalancing) — like the U.A.E., Trump, Jared Kushner and Bibi Netanyahu — will push M.B.S. into a war abroad and at home at the same time, and we could see Saudi Arabia and the whole region spin out of control at the same time. As I said, I’m worried.