The death Thursday of Saudi Arabia’s 90-year-old, long-ailing King Abdullah is hardly a surprise, nor are the ascensions of his 79-year-old brother Prince Salman as Saudi king and 69-year-old Muqrin, another brother, as crown prince. But the quick choice of Mohammed bin Nayef as the kingdom’s new deputy crown prince is surprising—and is significant domestically and internationally.

The 55-year-old Prince Mohammed is the first of the grandsons of Abdul Aziz, founder of modern Saudi Arabia, to be named in the line of succession. For nearly 60 years, one after another of Abdul Aziz’s more than three-dozen sons followed each other as king. Muqrin is the youngest surviving son.

Watching this band of brothers diminish in number and vigor left many inside the kingdom—and abroad—fearing that one day soon the next-generation princes would quarrel over succession and thereby risk destabilizing oil-rich Saudi Arabia.

Now the succession issue appears to be settled. This new leadership trio is likely to continue the kingdom’s foreign policies—specifically its regional competition with Iran, its distrust of the U.S., and its acceptance of low oil prices. At home, the main impact is likely to be further suppression of dissent; the brief spring of more tolerance when King Abdullah began his reign in 2005 is a distant memory.

Mohammed bin Nayef’s appointment surely will be welcomed by the U.S. and other Western nations that have worked closely with him over the past decade as the kingdom’s top officer in charge of curbing terrorism. Educated in the U.S. and fluent in English, Prince Mohammed was long seen as Washington’s preferred candidate among the younger princes who aspired to be king. As a result, some inside Saudi Arabia will see his selection as proof that the U.S., despite growing tensions with Saudi Arabia, still exercises a major say in who leads the kingdom. American support for him is a negative among young Saudi fundamentalists, who oppose Saudi ties with what they see as foreign infidels.

Since 2012 Prince Mohammed has been head of the powerful ministry of interior charged with internal security. The ministry has its own paramilitary force to guard key facilities, such as oil installations, and operates a sophisticated surveillance system monitoring Saudi citizens.

The ascent of this new-generation ruler could come sooner than expected. The new King Salman is said to suffer from Alzheimer’s, and Crown Prince Muqrin’s credentials to be king continue to be questioned by some in the royal family because his mother was only a Yemeni concubine of Abdul Aziz.

By contrast, the new deputy prime minister has two advantages: First, Prince Mohammed bin Nayef is part of the powerful family faction called the Sudairi (a Sudairi woman bore Abdul Aziz seven sons, including King Salman) who have dominated family affairs much of the past half-century. Second, Prince Mohammed has no sons, at least so far, which would make his ascension less threatening to other family factions.

What is clear is that the appointment of Mohammed bin Nayef as deputy crown prince and his cousin, Mohammed bin Salman, 30, the new king’s son, as defense minister and chief of his father’s royal court, injects clarity and vigor into the future succession of the Al Saud dynasty. The new deputy crown prince is credited by Saudis for keeping terrorism inside the kingdom at bay, but the new defense minister, who has been his father’s chief aide in recent years, is seen as inexperienced and arrogant and thus lacks public support. In the short term, though, the new leadership team faces serious challenges at home and especially abroad.

Even as the Al Saud princes buried their late king and then gathered after the day’s fifth and final prayer required of Muslims to pledge their bay’ah or allegiance to the new king, crown prince and deputy crown prince, Iranian-backed Houthi rebels had evicted the Saudi-supported leader of neighboring Yemen. (And at home, in Medina, a Saudi jihadist was shot attempting to storm a building housing security agencies.)

The kingdom’s efforts to confront and curb Iranian influence will continue unabated. In particular, the Saudis will continue to accept lower oil prices, a tactic that is helping to bankrupt Iran. Efforts to secure U.S. cooperation against the Islamic State terror group, or ISIS, in Syria and Iraq will also continue, as will the kingdom’s disappointment that the Obama administration is doing little to remove Iran’s ally, Bashar Assad, in Syria. Given the late Saudi king’s prolonged poor health, Salman as crown prince was involved in most of the kingdom’s foreign-policy decisions; he is unlikely to change much, unless he decides to be even tougher on Iran.

King Salman, who served more than 50 years as governor of Riyadh, the kingdom’s most conservative city, had the role of maintaining strong relations with the Wahhabi religious scholars whose support legitimizes Al Saud rule. These religious leaders deeply oppose Iran’s brand of Shiite Islam, as does the new king—unlike his predecessor, who at least advocated religious tolerance even for Shiites.

Notwithstanding concerns over King Salman’s health, he has a reputation as a hard worker (he once told me that he met 700 visitors in one day), a religious conservative and a tough-minded autocrat. Indeed, in a 2010 interview in his Riyadh office, he explained why Saudi Arabia cannot contemplate democracy. “If Saudi Arabia adopts democracy, every tribe would be a party” and the country would be ungovernable.

Beyond the focus on Iran, the Saudi regime is deeply worried that young Saudis, often educated but unemployed, will be attracted to ISIS’s call to fight in Syria and Iraq and to establish a true Islamic caliphate that would recapture the holy cities of Mecca and Medina. Obviously, this is a call for the dissolution of Saudi Arabia. The government has imposed mandatory 20-year sentences on Saudis who go abroad to fight, but that hasn’t eliminated the appeal of ISIS propaganda.

One Saudi imam told me during a visit in November that his son is begging to go to Syria to join ISIS. While the imam says he is discouraging the teenager, he acknowledged that he finds the ISIS call for a caliphate “exciting.” Like all too many Saudis, he sees the Al Saud as too worldly, while another group of Saudis argues that the rulers are too religiously conservative.

Prince Mohammed bin Nayef’s expanded role as minister of interior and deputy crown prince guarantees the use of tough antiterror policies. The prince survived a 2010 attempt on his life by a terrorist who blew himself up in the prince’s home without wounding the intended victim. Yet the prince has also been responsible for the kingdom’s efforts to rehabilitate terrorists by providing religious training and, if they convincingly recant terrorism, giving them a job, a car and a wife.

Having settled the generational succession issue, the Al Saud monarchy now faces the much tougher challenge of preserving its rule in a region racked by radicalism, conflict and chaos—and at home a people divided between those who want more modernity faster and those who want to return to the fundamentalism of Islam’s seventh-century founding.