Saudi Arabia, America’s oldest ally in the Middle East, is in the midst of the most profound changes in decades. The leadership is going through an unprecedented generational change and has adopted an aggressive foreign policy. The driver of change is the king’s favorite son, Deputy Crown Prince and Minister of Defense Mohammed bin Salman.

MBS, as he’s often called, is 30 years old, remarkably energetic, and very ambitious. King Salman has promoted him to an array of powerful positions and concentrated power in his hands quickly. In addition to being third in the line of succession behind the king and his cousin Crown Prince Mohammed bin Nayef, he often acts as the country’s top diplomat and he chairs the committee that sets economic and energy policy. He acquires new titles and responsibilities every week. Late in April he became the Saudi chief of a new cooperation council with Jordan, for example, with promises this will lead to stepped-up Saudi financial aid to Jordan.

The prince is the author of “Saudi Vision 2030,” an ambitious plan to wean the country of its dependence on oil income and create a more diverse economy. On May 7 the king issued 51 royal orders restructuring the government to implement his son’s plan, including sacking the oil minister, Ali Naimi, who had run the portfolio for two decades. The new orders also seek to encourage more foreign pilgrimage to the two holy cities of Mecca and Medinah by highlighting the opportunity for pilgrimage not just during the traditional Haj holy month, but year-round as well. Encouraging tourism is a major part of “Vision 2030.” All of the changes bear MBS’s stamp.

MBS effectively makes Saudi oil policy now. He sabotaged Naimi’s efforts to freeze or reduce OPEC oil production last month. His plan to open ARAMCO to outside investment is the centerpiece of “Vision 2030.” Oil is being used as a weapon by keeping production high to keep Iran from getting an oil bonus after the nuclear deal lifted sanctions.

The king has other and older sons with more experience than Prince Mohammed. One is Saudi Arabia’s only astronaut and another is governor of Medinah. But King Salman apparently has unique confidence in the young prince who controls access to his father and the Royal Court.

Other Saudis have been given great responsibility at an early age before. The modern kingdom’s founder, Abdelaziz ibn Saud, captured Riyadh when he was only in his late twenties. His son Faisal represented the kingdom after the First World War in London and Paris at the age of 14 and commanded an army three years later in battle. Prince Bandar became ambassador to the U.S. in his early forties. But MBS’s rise is unique for an heir to the throne in the last half-century. He is the symbol of youth in a nation where most of the population is his age or younger.

The prince is also the hand behind the creation of a new Islamic military alliance based in the kingdom. Some three dozen countries have joined. The prince envisioned the alliance as both a counter to terrorist groups like the so-called Islamic State and al Qaida as well as a counter to Iran and its allies like Hezbollah and Bashar Assad. It held large military exercises called “Northern Thunder” in the kingdom this winter.

MBS is also the architect of Saudi Arabia’s year-old war in Yemen. Initially it was called Operation Decisive Storm but then the war settled into a stalemate so the name was changed. The Saudis and their allies, especially the United Arab Emirates, captured the southern port of Aden but have been unable to wrest control of the capital Sanaa from Zaydi Shia rebels called Houthis and their partner, former Yemeni President Ali Abdullah Saleh.

A fragile cease-fire began last month. Political talks are underway in Kuwait between the rival Yemeni groups but there has been little progress. Meanwhile the Saudis and Emiratis have driven al Qaeda out of several cities along the southeast coast of Yemen. Al Qaeda in the Arabian Peninsula is regrouping and is far from destroyed. But it no longer is the main beneficiary of the war.

The Yemeni people have paid an enormous cost. Both sides have been guilty of egregious violence. The Saudi blockade has left millions of Yemenis at risk of malnutrition and without medical help. The rebels have starved the city of Taiz for months.

The Saudis claim they acted to prevent Iran from creating a puppet regime on the kingdom’s southern border. They were concerned when the Houthis set up direct air links from Sanaa to Tehran and offered use of the port of Hodeida to Iran. Hezbollah and Iran have provided some military advisers to the Houthis, but their influence on the rebels is limited.

The king and his son are pro-American but disenchanted with President Barack Obama. He has sold the kingdom over $100 billion in arms on his watch, according to the Congressional Research service. Obama has backed the Saudi-Yemen war with diplomatic, logistical, and intelligence support. U.S. advisers are now on the ground fighting al Qaeda.

But the Saudis cannot forgive Obama for abandoning Egypt’s President Hosni Mubarak in 2011. If one autocrat could be thrown under the bus, who might be next? They don’t like the Iran nuclear deal and believe Obama has been indecisive in Syria. MBS says he wants America to do more, not less, in the region. He is courting American journalists and think tanks.

King Salman has already dismissed one succesor. His half-brother, Crown Prince Muqrin, was removed from office a year ago without warning or explanation. The 80-year-old king could remove the current crown prince, his nephew Prince Mohammed bin Nayef, and elevate MBS at any time. The old guard in the royal family, which believes MBS is reckless and inexperienced, won’t like it, but they have few options to resist. If the king does put his son in the crown prince position the kingdom will skip a whole generation. It’s already been a remarkable journey for MBS.

This piece was originally published in The Daily Beast.