When the late King Abdullah appointed his half-brother, Moqren bin Abdul Aziz, as deputy crown prince last year, he added an unusual rider. The decree stated: “Nobody can change this decision.” Well, his successor King Salman just has.

I wrote at the time of the decree: “There is nothing to stop Salman going to the Bay'ah either collectively or individually and reversing the decree in the event of the king's resignation, death or incapacitation.” This is what happened in an early dawn decree on Wednesday. When Salman became King I also wrote that if he left Moqren in place, he would remove him later. This too happened.

This cabinet reshuffle proves beyond doubt that all power still resides in the king, and that one king can override the legacy of his predecessor. Institutional mechanisms like the Allegiance Council are but straws in the prevailing wind.

Salman has cleared out all but one of the last remaining supporters of the old regime, and completed the succession from one generation to another. Moqren was not a powerful figure in his own right. He was placed there by Abdullah to keep the seat warm for his son Prince Meteb, who remains head of the National Guard and a minister.

How much longer, we will see. Some sources say that Salman is now seriously considering abolishing the National Guard ministry, which Abdullah latterly established. This would bring it back into the fold of the Defence Ministry - which of course is headed by Salman’s son Mohammed.

Moqren was used as a link man to Abdel Fattah al-Sisi’s regime in Egypt. Moqren represented Saudi Arabia at the international donor conference in Sharm El Sheikh, not Salman. And when the Egyptian leader wanted to apologise to his Saudi paymasters about the contents of the leaked tapes, in which Sisi himself said: "Man, they [the Saudis] have money like rice," the Egyptian ambassador to Saudi Arabia was seen by Moqren first, before Sisi himself hit the phones.

Saud bin Faisal’s exit as foreign minister on Wednesday, was, I understand, planned a long time ago. Bin Faisal, the world’s longest-serving foreign minister, had run out of road, and even 40 years experience as a time server could not keep him on it. Even he found it difficult to smoothe over the contradictions of serving Abdullah and his successor Salman. Under Abdullah, he led diplomatic efforts to besiege Qatar. Under Salman, he appeared relaxed about the Muslim Brotherhood, and even had a public row with Sisi over Putin’s support for Syria. You can’t be an advocate for both policies.

His replacement by the former Washington ambassador Adel bin Ahmed Al-Jubeir, who is close to the US administration and is considered a liberal, is a sign of Salman’s foreign policy orientation: whatever else, Salman wants to keep America close. Al-Jubeir is only the second foreign minister to be appointed from outside the ranks of the House of Saud.

Salman completed his clear-out of Abdullah’s people through a whole series of ministerial changes. Few traces of the old regime are left.

Who then are the winners and who are the losers? These changes will be music to the ears of Turkey and Qatar, with whom Mohammed bin Nayef - now next in line to the throne - has close relations. If that is the case, the main losers are the United Arab Emirates and Egypt.

We already know that relations between Mohammed bin Nayef and Mohammed bin Zayed, the Crown Prince of Abu Dhabi and de facto Emirati ruler are fraught. Bin Zayed has visited Riyadh three times since Salman came to power in January, and only met the king himself once. The chief reason for their fallout is the current Saudi war in Yemen, where bin Zayed is still backing the forces of the ousted strongman Ali Abdullah Saleh, and still hosting his son Ahmed Ali in Abu Dhabi. Saudi Arabia is now bombing forces loyal to the Salehs.

The other big loser is Egypt, who has lost both Moqren and bin Faisal, both linchpins of Cairo's relationship with Riyadh.

For the kingdom itself, the succession is now complete. The two men running the country and its wars are Mohammed bin Nayef, the new crown prince, and Salman’s young son, Prince Mohammed bin Salman. Hidden among the young prince’s plethora of portfolios (he is defence minister, head of the court, head of the Council for Economic and Development Affairs) one factor is more important than all the others.

The two Mohammeds are cousins, but Salman’s son is very respectful of bin Nayef. It goes back to the close links bin Nayef’s father had with Salman himself. In fact, Mohammed bin Salman goes out of his way to show his respect for bin Nayef, and recently kissed his hand in public. But Mohammed bin Salman has one advantage over his elder cousin, which is that bin Nayef does not have a son. The line of succession, which is so important in these decrees, therefore will be carried on through Salman’s own son, and not through bin Nayef. In this sense what happened on Wednesday will have implications for decades to come.

Egyptian President Abdel Fattah al-Sisi (C) meeting with Saudi Defence Minister Prince Mohammed bin Salman bin Abdul Aziz al-Saudi (L) and Egyptian Defence MinisterGeneral Sedki Sobhi in Cairo (AFP)

The big question is what Salman will do with the power he now wields. Regionally the kingdom is now fully committed to a contest for power and influence with Iran.

In Yemen, Iraq and Syria, to the south and north of its borders, Saudi Arabia is attempting to show Iran that there is no more vacuum in the region for them to fill. The outcome of this giant contest is yet to be decided. It may presage a further decade of proxy conflict, which could be at least as bloody as Iraq’s war with Iran, bleeding the wealth of both countries.

Or Iran and Saudi Arabia could reach an accommodation and be the joint architects of a regional peace. Both now have a common ally in Turkey, with whom Iranian trade continues to flourish. But the dimensions of this conflict and its significance can no more be in doubt. Nor can Saudi Arabia’s resolve to be a military power on the frontline itself.

Saudi Arabia has long since stopped paying others to do its dirty work. It has become a frontline fighting power in both Yemen and Syria - providing arms and logistics and doing the fighting itself - and the effects are being felt. In Syria, the change in Saudi tactics and its co-ordination with Turkey and Qatar and the groups they fund are already being felt in the advances of rebel forces against Bashar al-Assad’s forces in Idlib.

This is a sea change from just three months ago when Assad’s forces were advancing and Aleppo was about to fall. Now, for the first time, three powerful rebel groups, none of them angels, Jabhat al-Nusra, Ahrar al-Sham, and Jaish al Islam, have stopped fighting each other and are co-ordinating their actions. One Iranian commentator, Amir Mousawi, has even suggested that Assad should move his capital to Tartus, the Alawite stronghold. But in Syria, the so-called Salman doctrine is taking effect.

Mohammed bin Salman’s air campaign in Yemen can still go either way. The bombing is now more against Yemeni military targets loyal to the ousted dictator Ali Abdullah Saleh than it is against the Houthis. Both are on a revenge mission. For the Houthis, this is payback time for six wars with the government that have devastated their northern homeland. Even though Saleh mounted the wars against the Houthis, he too wants to bring Yemen to its knees if he cannot have his way by installing his son as president. Saleh appears to have lost all political reason, and according to those still in contact with him, wants to bring the house he built down on himself. While the Saudi campaign is supported in the south, the Houthis are installed in Sanaa, and there appears to be no-one ready for the moment to fight them there.

The key challenge for the Saudis is to decide on a leader who can unite anti-Houthi and anti-Saleh forces and lead the military campaign on the ground in Yemen. The Muslim Brotherhood-linked Islah movement will not fight with all their might until they feel they have a clear mandate to do so, and know which direction Riyadh is heading.

The larger challenge facing Salman is how he will use the absolute power he now has, and whether he will take advantage of a younger leadership to institute real democratic change. The kingdom desperately needs more transparency in its decisions, a bigger distribution of wealth, and to include more groups in the decision-making process. The late King Abdullah’s one achievement was to send tens of thousands of bright young students abroad for their higher education. They are back now. Can the kingdom absorb what they have learned? Salman’s legacy will hinge on the answer.

- David Hearst is editor-in-chief of Middle East Eye. He was chief foreign leader writer of The Guardian, former Associate Foreign Editor, European Editor, Moscow Bureau Chief, European Correspondent, and Ireland Correspondent. He joined The Guardian from The Scotsman, where he was education correspondent.

The views expressed in this article belong to the author and do not necessarily reflect the editorial policy of Middle East Eye.

A picture in a street of the Saudi capital Riyadh shows a billboard bearing an image with a soldier and Saudi King Salman bin Abdulaziz and reading "my country, we all protect your soil", April 15, 2015 (AFP)