The Middle East being the Middle East, everything is interrelated. What happens in the region impacts Yemen and what happens in Yemen impacts the region. The crisis in Yemen, like many conflicts in the Middle East, did not originate with the power struggle between Saudi Arabia and Iran, but inevitably get sucked into it.

Yemen was a Saudi problem long before it took on the mantle of a Saudi-Iranian proxy war and it may be the conflict that is most important and most sensitive for the kingdom. It also may be the proxy war that comes to haunt Saudi Arabia the most. Beyond cross-border tribal relationships, Yemen, a devastated country where recovery and reconstruction is certain to be a slow process, is likely to have a next generation that will be deeply resentful of Saudi Arabia with all the political and security implications that go with that.

More immediately, two recent factors stick out that potentially have significant geopolitical consequences. First, the recent meeting between the crown princes of Saudi Arabia and the United Arab Emirates, Mohammed bin Salman and Mohammed bin Zayed, with leaders of Yemen’s Islamist Islah party in the wake of the killing of former Yemeni President Ali Abdullah Saleh. The presence of Mohammed bin Salman at the meeting was far less remarkable than that of Mohammed bin Zayed and it is not clear what it means. It is Mohammed bin Zayed rather than Mohammed bin Salman who is truly uncomfortable with any expression of political Islam and certainly with any link to the Muslim Brotherhood. Islah remains an Islamist party even if it announced in 2013 that it had cut its ties to the Brotherhood.

The question is whether Mohammed bin Zayed, who for the almost three years of the Yemen war opposed Saudi cooperation with Islah, sees an alliance with the party as an opportunistic one-off move or whether it signals a shift in policy that could be repeated elsewhere in the Middle East. If so, that would have consequences for the dispute with Qatar and there is no sign of that. In fact, Saudi Arabia signalled days after the meeting that there was likely to be no quick end to the dispute with Qatar by declaring its closed border crossing with the Gulf state permanently shut. Similarly, recent satellite pictures show that the UAE air force is gearing up for greater military engagement against Islamists in Libya. As a result, the significance of the meeting is likely to be limited to Yemen.

Nonetheless, the way the meeting was arranged is significant and tells a story that goes far beyond Yemen. The crown princes sent a private plane to Istanbul to pick up the Islah party representatives from an Islamic summit called to discuss US President Donald J. Trump’s decision to recognize Jerusalem as the capital of Israel. It was a summit the two men decided not to attend and at which they were represented by lower officials. The message was: Jerusalem and the Israeli-Palestinian conflict was not their priority and their opposition to Mr. Trump’s move was skin deep. Their priority was the war in Yemen and the larger regional battle with Iran for dominance of the region.

In some ways, Saudi Arabia and the UAE’s risky strategy has already backfired. It has given the Brotherhood, violently suppressed in Egypt, outlawed in much of the Gulf and marginalized elsewhere in the region, a new lease on life. Mr. Trump’s decision offered the Brotherhood an issue to rally around in an Arab world intimidated and cowed by the violence, repression, insurgencies and civil wars that have characterized it since the 2011 popular Arab revolts that toppled the leaders of Tunisia, Egypt, Libya and Yemen.

With a long history of opposition to a US-mediated Israeli-Palestinian peace process, the Brotherhood has emerged in the front lines of many of the protests against the president’s recognition of Jerusalem. Muslim Brothers organized the biggest popular protest in Jordan in a decade and demanded the closure of the Israeli embassy in Amman. Beyond leading demonstrations in Kuwait, Brother members of parliament called on the government to review its ties with Washington and disinvest from the United States.

Mr. Trump’s move has also strengthened Brotherhood offshoots like Hamas, the Islamist group that controls the Gaza Strip. Confronted with protests against its inability to break a crippling, economic stranglehold by Egypt, Israel and the Palestine Authority that starved the Strip of electricity and forced government workers to go unpaid for months, Hamas was forced by the UAE and Egypt to enter into a reconciliation agreement with Palestinian President Mahmoud’s Abbas’ Al Fatah movement and entertain an independent governance position for powerful but controversial, Abu Dhabi-backed former Palestinian security chieftain Mohammed Dahlan.

The second factor are Houth ballistic missile strikes, including the firing in November of a projectile at the international airport of the Saudi capital Riyadh, subsequent claims and denials of a Houthi missile fired towards the UAE, the December 2017 targeting of the Al Yamama palace of the Saudi royal court as King Salman and Prince Mohammed were chairing a meeting of the kingdom’s leaders, and the Houthi threat of further attacks. A Saudi military spokesman said the kingdom had intercepted 83 ballistic missiles since the Yemen war started almost three years ago.

There is little doubt that the Saudi-UAE intervention in Yemen has fortified ties between the Houthis and Iran. Yet the recent theatrical display of Houthi missile parts and other weaponry that was made possible by Saudi Arabia and the UAE left their provenance in doubt. There was no smoking gun that established beyond doubt that Iran could be held responsible for the missile strikes. The missiles and other items could well have originated in Iran, they could also have come from elsewhere. Whether supplied by Iran or not, United Nations monitors reported to the Security Council that remnants of ballistic missiles launched into Saudi Arabia by Houthi rebels appeared to have been designed and produced by Iran.

Iran insisted that it had not supplied the missiles, but said it would continue to support the Houthis and other “resistance forces” in the region. “Victory in Iraq, Syria, Lebanon and Yemen will continue as long as the resistance coalition defends its achievements. And as long as necessary, we will have a presence in these countries…We must assist these countries and establish a barrier against the American influence,” said Ali Akbar Velayati, a senior aide to Iranian Supreme Leader Ali Khamenei and former foreign minister.

Mr. Velayati’s remarks appeared to contradict Iranian President Hassan Rouhani’s denial that Iran had a military presence in Yemen and was assisting the Houthis. So did an earlier admission by Islamic Revolutionary Guards Corps commander Mohammad Ali Jafari that Iran was providing the Houthis with “advisory military assistance,” the phrase the Islamic republic used for its support of militias in Syria and Iraq.

Evidence of Iranian military support for the Houthis has been mounting. The Australian government released in January pictures of anti-armour weapons that were seized off the Yemeni coast and had been manufactured in Iran. A report in late 2016 by Conflict Armament Research concluded that a weapons pipeline extended from Iran to Yemen as well as Somalia that involved “transfer, by dhow, of significant quantities of Iranian-manufactured weapons and weapons that plausibly derive from Iranian stockpiles.”

The Houthis, a fiercely independent actor have, irrespective of the degree of Iranian support, repeatedly demonstrated, however, that they do not take orders from Tehran and at times ignore its advice. Iran opposed the Houthi move on the Yemeni capital of Sana’a to no avail and was against a Houthi advance in the south. The Houthis could well against Iran’s will throw another monkey wrench into the fragile Middle East mix if they continue to target Saudi and/or Emirati cities. The attacks would ultimately elicit a harsh response. The question is who would respond and what would the target be.

The answer seems at first glance obvious. It would be a Saudi and/or UAE response and the target would be the Houthis in Yemen. The deployment of a new, American-trained and supplied Saudi National Guard helicopter unit to the kingdom’s border with Yemen suggests an escalation of the Saudi-UAE campaign. The Pentagon said 36 AH-64E Apaches, 36 AH-6i Little Birds, and 72 Sikorsky UH-60M Blackhawks bought from the US at a cost of $25 billion would be used to protect Saudi Arabia’s borders and oil infrastructure. The deployment constitutes the first expansion of the Guard’s mission beyond protecting the ruling Al Saudi family, guarding oil facilities, and providing security for the holy cities of Mecca and Medina since Prince Mutaib bin Abdullah, a son of former King Abdullah, was relieved of his command of the Guard in November and detained by Prince Mohammed on corruption charges alongside other princes, senior officials and prominent businessmen.

The retaliatory target could, however, also be Iran and the response could be one in which the United States participates. The implications of such an escalation could be massive. “An Iranian missile fired at Riyadh sheds light on an important bottom line dynamic in the region: the Saudis have a far superior air force, defence system and navy than the Iranians. They have a better equipped military intelligence apparatus and far superior munitions…(Iran) has been wreaking havoc in the Middle East on its own terms and drawing on its own strengths. It must realise that such recklessness could cause its regional adversaries to draw on their competitive advantages,” said Middle East analyst Mohammed Alyahya.

A broader regional military altercation would occur at a moment that emotions are raw in the wake of Mr. Trump’s decision on Jerusalem and because protesters are already on the streets of various Middle Eastern cities. A strike against Iran involving the United States could turn fury about Mr. Trump’s Jerusalem decision against Arab leaders who would be seen to be cooperating with the United States and willing to sacrifice Palestinian rights to work with Israel. Soccer fans in Algiers who were protesting against the decision recently provoked Saudi Arabia’s ire by carrying placards depicting Mr. Trump and Saudi King Salman as two sides of the same coin. While the protests in recent week were primarily directed against the United States and Israel, they often had an undertone of criticism of Arab regimes that were seen to be meek in their response to Mr. Trump’s decision or in cahoots with the United States.

Ironically, differences among Arab leaders about how to respond to Trump’s Jerusalem decision may have temporarily prevented the Saudi Crown Prince from adding Palestine to a string of failed foreign policy moves aimed at escalating the kingdom’s proxy war with Iran. Prince Mohammed’s devastating intervention in Yemen, botched effort to force Lebanese Prime Minister Saad Hariri to resign, and hamstrung boycott of Qatar have backfired and only strengthened the Islamic republic’s regional influence.

Inadvertently Palestinian President Abbas and Jordanian King Abdullah did Prince Mohammed a favour when they reportedly rejected pressure by the prince not to participate in the summit of Islamic countries in Istanbul. Mr. Abbas may have further shielded the Saudi leader when his refusal to further accept the United States as a mediator was adopted by the summit.

The two leaders’ stand, coupled with the summit’s rejection of Trump’s move, make it more difficult for Saudi Arabia and the UAE to endorse any resolution of the Israeli-Palestinian conflict that does not recognize East Jerusalem as the capital of Palestine. The problem is that the Saudi and UAE crown princes run the risk of misreading or underestimating public anger and frustration in significant parts of the Arab and Muslim world.

The Saudi crown prince responded to the two leaders’ defiance by briefly arresting billionaire Jordanian Palestinians businessman Sabih al-Masri, who also has Saudi citizenship. “The Saudi detention of Masri was a crude but brutal political message to…King Abdullah and…President Mahmoud Abbas on how to behave on the Jerusalem issue and regional alignments. Riyadh wanted to signal to the Jordanian and Palestinian leaderships that it could swiftly cripple their economies and trigger existential crises in which banks would suffer terminal runs, the governments would fail to pay their employees, and the economies would sputter to a halt,” said Middle East scholar and analyst Rami G. Khouri.

Disagreement in the Arab world over how to respond to Mr. Trump’s Jerusalem decision and Mr. Abbas’ defiance has taken on even larger significance with the battle over a United Nations General Assembly vote on the issue. Mr. Abbas instructed his diplomatic representatives to ensure the passing of a resolution that condemns the US move despite a US threat to cut off aid to countries that vote in favour and at the risk of the Trump administration deciding to close the office of the Palestine Liberation Organization (PLO) in Washington.

How Saudi Arabia and the UAE vote could impact relations with the United States and the degree to which they are sensitive to criticism of their conduct of the Yemen war, if they vote in favour of the resolution and Mr. Trump acts on his threat. In another indication of Saudi and UAE priorities, Bahraini Foreign Minister Khaled Ben Ahmed hinted at the Gulf states abstaining in the UN vote in a move that likely would contradict public opinion, Mr. Ben Ahmed, referring to Iran, tweeted that “it’s not helpful to pick a fight with the USA over side issues while we together fight the clear and present danger of The Theo-Fascist Islamic republic.”

Saudi, UAE and Bahraini willingness to break with a long-standing consensus in the Arab and Muslim world would have likely been strengthened with the publication of Mr. Trump’s national security strategy that, like Saudi Arabia and the UAE, prioritizes combating “jihadist terrorists;” preventing the domination of “any power hostile to the United States,” an apparent reference to Iran and Iranian-backed proxies; and ensuring “a stable global energy market.”

The link between Israeli-Palestinian peace making and Iran, and by extension Yemen, is, moreover, likely to become undeniable when Mr. Trump next month must decide whether to uphold the 2015 international agreement with Iran that put severe restrictions on its nuclear program in exchange for the lifting of sanctions.

Under US law, Mr. Trump has to certify Iranian compliance every three months. In October, Mr. Trump refused to do so. He threatened to pull out of the agreement if Congress failed to address the accord’s perceived shortcomings within 60 days. Congress has refrained from acting on Mr. Trump’s demand that Congress ensure that Iranian compliance involves accepting restrictions on its ballistic missile program that is primarily designed to counter perceived US and Israeli threats, and support of regional proxies. A study by the International Institute of Strategic Studies (IISS) concluded that to counter challenges posed by regional insurgencies, failing states and extremism, Iran was likely to expand its weapons acquisition program to include surface- and air-to-air missiles, advanced fighter aircraft, tanks, advanced mines, and anti-ship cruise missiles.

Concern that proxies that fought in Syria could turn their attention to Yemen was enhanced by Ali-Reza Tavasol, a founder of the 20,000 man-strong Fatemiyoun Division, an Iranian-led Afghan Shiite militia group. “Our war is an ideological war and does not recognize geography and borders. Anywhere oppressed people need help, we will be present there and assist them,” Mr. Tavasol said. Mr, Tavasol’s statement echoed earlier remarks by Ismail Ghani, the deputy commander of the Revolutionary Guard’s Quds Force, who asserted that Fatemiyoun fighters did “not recognize borders to defend Islamic values.” Afghan officials alleged that some Fatemiyoun fighters has already been dispatched to Yemen.

At the end of the day, the Saudi-Iranian rivalry is being fought on the back of the Yemenis who are paying a horrendous price. That is unlikely to change as long as Saudi Arabia sees its struggle with Iran as an existential battle. And to be fair to the Saudis, they have good reason to perceive Iran as an existential threat. Not because Iran engages in asymmetric warfare by using proxies, supporting groups like the Houthis or propping up the regime of Syrian President Bashar al-Assad.

But because post 1979-Iran, even if t were to only sit back and do nothing, poses an existential threat in much the same way that the popular Arab revolts of 2011 posed an existential threat. Iran experienced, alongside Russia, the 20th’s century only true revolution in which a regime and a political system was overthrown. It was a revolution that toppled a monarch and an icon of the United States. It was a revolution that introduced an Islamic system of governance that has whatever limited degree of popular sovereignty. That is the threat, it constitutes an alternative to an absolute monarchy that claims religious legitimacy and is seeking to ensure its survival.

And if that were not enough, Iran is one of three Middle Eastern nations that, irrespective of what state of disrepair they may be in, have the building blocks to be regional powers. The other two are Turkey and Egypt. They have large populations, huge domestic markets, battle-hardened militaries, an industrial base, highly educated populations, geography and a deep sense of identity rooted in empire and/or thousands of years of history. Saudi Arabia has money and Mecca.

If Saudi Arabia and the UAE learnt a lesson during the era of US President Barak Obama, it is that nothing is permanent and that countries need to assert themselves. Yemen is an expression of that lesson. Mr. Trump has given the kingdom and the emirates the umbrella they needed. Saudi regional power is to a large extent dependent on an Iran that is hampered by US-led efforts to contain it. Again, to be fair, the UAE has been better than the Saudis at exploiting the opportunity.

Saudi Arabia has so far ended up with mud in its face. The war in Yemen is backfiring and threatens to create even bigger challenges in the longer term. In a toughening of US criticism of the kingdom’s conduct of the war, Mr. Trump’s nominee for the post of the State Department’s legal counsel, Jennifer Newstead, suggested that Saudi Arabia could be violating U.S. and international law by restricting the flow of humanitarian aid in Yemen. British international development secretary Penny Mordaunt issued a similar warning. A determination that the kingdom is in violation would, amid widespread international criticism of the humanitarian crisis in Yemen sparked by Saudi military action, put at risk US support for the intervention, involving US assistance in mid-air refueling of Saudi and Emirati fighter planes, the provision of precision-guided munitions, and the sharing of intelligence.

Moreover, with dissent repressed, it is difficult to gauge what public opinion in the kingdom is. Prince Mohammed has so far delivered long-overdue social changes but has yet to deliver on his economic reform plans. There is good reason to question the degree to which he will be able to deliver, not only because there are legitimate questions about his plans but also because of the way he has gone about implementing them. The recent arrests of scores prominent Saudis under the mum of an anti-corruption campaign and the financial settlements being negotiated for their release raises questions about what kind of checks and balances a new Saudi Arabia would offer and defy the principle of the rule of law.

No doubt, Prince Mohammed is an enormously popular figure. The problem is that he has created enormous expectations that have not been managed. Moreover, 40 years of Sunni Muslim ultra-conservatism rooted in a history of at least 200 years of ultra-conservative thought cannot be erased with the stroke of a pen. Prince Mohammed’s social changes are as popular as they are controversial. In a recent survey, young Saudis said they wanted change: they wanted to date women, they wanted to party, they wanted to drive fast cars, and, yes, they wanted good paying jobs. When asked whether they realized that those same rights would apply to their sisters, they pulled back. In a recent illustration of contradictory attitudes, a Saudi beauty queen withdrew from a Miss Arab World contest after being attacked and threatened online. Similarly, Saudis want jobs but are unprepared for a merit-driven labour market rather than one that offers cushy government jobs.

The long and short of all of this is that the war in Yemen cannot be seen independent of the convulsions of change that have enveloped the Middle East in a convoluted and often violent process with no end in sight. The wars in Syria and Iraq are dying down. Yet, without policies that ensure that all groups in society feel that they have a stake in society, the seeds for renewed conflict are being sown. The same is ultimately also true for Yemen. Whatever one thinks of Mr. Obama, he got it right when he told journalist Jeffrey Goldberg that Saudi Arabia will have to learn to share the Middle East with Iran.

This article is adapted from a lecture originally delivered at the U.S. Middle East Institute seminar.