In very recent memory, the true god of Saudi Arabia was stability. The kingdom was very conservative, not just in religion and politics, but in the way it did things: slowly, cautiously, close to fossilized, with payoffs in power and money to buy calm.
That was then.
Last weekend was the shock-and-awe moment that showed how much everything has changed.
Consider: On Saturday, a Saudi Who's Who including 11 princes  of the royal line were rounded up. The Riyadh Ritz-Carlton was converted into the world's most well-appointed detention facility. The most powerful shark caught in the net was Prince Mutaib bin Abdullah, son of the late King Abdullah and deposed head of the National Guard, the kingdom's largest military force.
Officially, it was a crackdown on corruption. Unofficially, Crown Prince Mohammed bin Salman is eliminating competition.
The same day, Lebanese Prime Minister Saad Hariri announced  his resignation—from Riyadh, on Saudi television. The style of the wording wasn't Lebanese, says political scientist Hilal Khashan of the American University of Beirut. “Hariri was summoned to Riyadh, and he was coerced to read his resignation statement [which] was written by the Saudis,” Khishan told me. The abrupt aggressive intervention bore the fingerprints, again, of Crown Prince Mohammed bin Salman, otherwise known as MBS.
It wasn't MBS's fault that a missile was fired that very day at Riyadh from territory in Yemen held by Iranian-backed Houthi rebels. But it was MBS who went on the air  to blame the attack directly on Iran, and it was apparently his decision to respond with a total sea and air blockade on Yemen. One consequence: The Red Cross said it couldn't deliver a shipment of cholera-prevention pills to Yemen, where 900,000 people are already suffering from the disease and seven million are on the edge of famine.
Then there's the matter of the helicopter crash the next day. One of the people killed was another prince, Mansour bin Muqrin, whose father had been crown prince for a few months in 2015 and was then deposed. The crash could really have been an accident, and a gruesome coincidence of timing. “I can't see why he was a particular threat,” says veteran Saudi watcher Joshua Teitelbaum of the Begin-Sadat Center at Israel's Bar-Ilan University, adding that “this isn't the Saudi way of doing things.” Suspicion of MBS will still vibrate through the kingdom and the region.
Mohammad bin Salman is “a young man in a hurry,” says Daniel Shapiro, the former U.S. ambassador to Israel, speaking with diplomatic care. MBS is “a young prince, not very experienced, and doesn't seem to be well educated,” says Teitelbaum.
The crown prince may be the man who will, at last, reform the sclerotic Saudi realm. Look, say the optimists, he has allowed women to drive cars, which counts as a radical move in the kingdom. Then again, he may be the impetuous heir who will shatter whatever is left of stability in the Middle East.
The backstory: Saudi Arabia's founder, King Abdulazziz, had several dozen sons by multiple wives. Since his death in 1953, the crown has passed from one of his sons to another. The brothers had children and became leaders of sub-clans. And since the reign of the second of the sons, Faisal, kings have held the realm together by building a balance “by dividing the military between various branches of family, and important ministries, and the courts,” Teitelbaum explains.
Foreign policy reflected the same balancing act. “The Saudi strategy,” says Teitelbaum, “has always been not to push things past the boiling point.”
The question, deferred for decades, was what would happen when rule passed to the last eligible brother. That era arrived in 2015. King Abdullah died and was replaced by Salman, then 79. One more brother, Muqrin, a mere 70 years old, was named heir to the throne. Just three months later, he was pushed aside in favor of the first crown prince from the generation of Abdulazziz's grandsons, a nephew of Salman, Mohammed bin Nayef.
Meanwhile, King Salman gave an expanding list of powerful roles to his son, starting with appointing him defense minister. Last June, MBS was named crown prince.
The recent arrests follow the same pattern: Salman and son are apparently aiming at replacing the old system of brothers with a new dynasty. In the process, they have “gone against the principle of balance, which gave a great deal of stability,” Teitelbaum says.
What's more, the dynastic battle takes place against the backdrop of internal and external challenges. The world drop in oil prices had made it urgent for Saudi Arabia to transform itself. The kingdom is “eating its foreign currency reserves,” says Meir Litvak, head of the Center for Iranian Studies at Tel Aviv University. The Saudis have to “change direction if they doesn't want to collapse in another 15 or 20 years.”
So who's in charge of the massive plans to create a high-tech economy and attract foreign investment? The crown prince, yet again. Cracking down on corruption could help bring investment. Creating a daily storyline of political instability could do exactly the opposite.
Regionally, the Saudi regime faces the steady rise of its rival, Iran. In the Syrian civil war, Iran is “unequivocally” the winner, along with Russia, says Litvak. In Iraq, Teheran now has “a major foothold.” Together, this creates the “land bridge” that Iran has sought to Lebanon and the Mediterranean.
But the way Mohammed bin Salman has handled foreign policy does not create confidence in his judgment. He's the architect of Saudi intervention in Yemen, which has turned into a quagmire. The Saudi attempt to isolate Qatar has failed.
And now comes MBS's newest gamble, the shake-up in Lebanon. The country was another example of uneasy balance. Hariri, the Sunni prime minister, represented Saudi interests. But he shared power—as the weaker partner—with Hezbollah, backed by Iran. In his resignation speech from Riyadh, Hariri blasted Iran and Hezbollah. Since then he has stayed in the Saudi capital, possibly under duress. Lebanese President Michel Aoun has said  he won't accept the resignation till Hariri returns.
What MBS hopes to gain is a matter of speculation. “I'm not sure how well thought out it is. It may be impulsive,” says ex-ambassador Shapiro. Possibly, the plan is to “shift all responsibility for Lebanon to Hezbollah and rally others including the United States to increase pressure—let's say, broader U.S. sanctions against the Lebanese banking sector,” or ending U.S. aid to the Lebanese Army.
The more extreme scenario is that the Saudi crown prince hopes that leaving Hezbollah in charge will lead to war with Israel, in which the Shi'ite organization would be battered. But that's a less likely outcome, says Litvak, “though in the Middle East it's hard to know.” Hezbollah still has troops tied up in Syria. Political scientist Khashan, in Beirut, assesses that “nobody in Lebanon is interested in escalation.” In a speech on Sunday, he notes, Hezbollah leader Hassan Nasrallah “was extremely careful to play down the content of Hariri's resignation.”
In either case, MBS's move shows yet again his willingness to gamble on shaking things up.
He does have a cheering squad for his approach. President Trump responded to Saturday's round-up by tweet, “I have great confidence in King Salman and the Crown Prince of Saudi Arabia, they know exactly what they are doing.”
This doesn't mean that MBS coordinated his moves with Washington. But Trump likes his style of knocking things over. For anyone else watching Saudi Arabia, this is the worst endorsement the aggressive young prince could get.