In the last decade, the Middle East has been living through a political convulsion of historic proportions. Regimes that once appeared immovable have been destroyed or receded. New forces have risen and are making war over the ruins. The result of the

A cartoon in the English-language Saudi daily Arab News explains why an Arab coalition is intervening in Yemen.

In the last decade, the Middle East has been living through a political convulsion of historic proportions. Regimes that once appeared immovable have been destroyed or receded. New forces have risen and are making war over the ruins.

The result of the effective eclipse in recent years of the states of Iraq, Syria and Lebanon has been the emergence of a large and chaotic conflict in the contiguous area once covered by those states. The failure to develop coherent state-loyal national identities in the areas in question has meant that once central authority disappears, a political- military competition based on forces assembled according to ethnic and sectarian identity emerges. A sectarian conflict is, as a result, now raging between the Iraq- Iran border and the Mediterranean. This dynamic of conflict has now extended to Yemen.

As non-Arabs and non-Sunnis, the Iranians are outsiders twice over in the largely Sunni, Arabic-speaking Middle East.

In this maelstrom, the Iranians and their clients have emerged as the single most formidable alliance. Why is this? What are the particular advantages enjoyed by the Iranians and their proxies in this contest? What explains the recent belated, but determined, Saudi-led Sunni reaction to the Iranian advances? And what are the implications of the apparent moves toward a nuclear deal and lifting of sanctions on Iran toward Tehran's actions in the region? Iran has, in its Revolutionary Guards Corps and its Quds force, an instrument perfectly suited for the moment that the region is currently passing through. The IRGC is an organization specifically created for the prosecution of proxy war and the mobilization and sponsorship of paramilitary clients.

The Sunni Arabs (or indeed any other regional actor) do not possess a comparable force. The result of the centralized commitment of Tehran and the skills of the IRGC is that the Iranians have been winning in a number of conflict arenas in the Middle East, and the Saudis and other Gulf countries have been becoming increasingly alarmed.

Lebanon

In Lebanon, the effective parallel state maintained by Hezbollah remains the strongest player in the country. Hezbollah is the prototype and still the strongest of Iran's proxies in the Arab world. Its strength, the absence of a military tradition among Lebanese Sunnis, and Lebanon's small size have enabled the movement to maintain its dominance in spite of the sectarian ferment to its east.

Hezbollah has played a vital role in the Syrian civil war and in the Iranian effort to keep its client in Damascus in power. The movement has lost around 1,000 fighters in Syria, including a number of prominent veteran commanders. It is thought to have some 5,000 men committed in Syria at any given time. Hezbollah's Syria commitment is testimony to the extent that the movement can ignore the wishes of any other Lebanese factor when answering to the call of its Iranian patrons. It is also, equally importantly, testimony to the ability of Iran to marshal all its regional assets to work together in a coordinated fashion for the interests of any one of them. This centralization is one of the greatest advantages possessed by Iran in its drive to dominate the region.

Syria

In Syria, Iranian commitment to the Assad regime has preserved it. Assad has not been doing well recently. In the south, rebels and Sunni Islamist fighters have captured the historic town of Bosra al-Sham. More importantly, in the north, a force led by Jabhat al-Nusra, the Qatar and Turkey- supported franchise of al-Qaida in Syria, in late March captured Idleb, the second provincial capital to be wrested from government control. The Islamic State (ISIS), ominously, is now gaining ground close to Damascus.

Despite this, the regime, a long-term client of the Iranians, remains the single most powerful element in Syria. It controls around 40 percent of the area of the country and about 60 percent of the population.

Iranian funds, manpower and military expertise have ensured the Assad regime's survival.

The continued provision of Iranian funds – reputedly at a rate of around $1 billion per month – and of Iranian manpower and Iranian military expertise is the single most significant factor in ensuring the Assad regime's survival.

The key problem for Assad throughout has been the shortage of reliable manpower willing to engage on his behalf. The commitment by Iran of its own personnel and that of its Lebanese and Iraqi proxies, and the creation by the Iranians of sectarian proxy militias for the regime (the National Defense Forces and others) have to a considerable degree addressed this problem.

Assad is not close to reconquering the entirety of Syria's territory, but he is also not in danger of falling. This is an Iranian achievement, not a Syrian one.

Iraq

In Iraq, the Iranians are taking a key role in the fight against ISIS. Some observers only half-jokingly now refer to Quds Force commander General Qasem Soleimani as the true ruler of that country.

Iranian-backed Shi'a militias have been playing the key role in the fight against ISIS in Iraq.

Soleimani has been intermittently present in Iraq, directing the mobilization of Shi'a militias against the ISIS threat, since last August. The three most powerful such militias, the Badr brigade, Asa'ib Ahl al- Haq and the Kata'ib Hezbollah, answer to his command rather than that of the Iraqi government. The government, meanwhile, is itself dominated by the Shi'a Islamist and pro-Iranian Dawa party.

The Shi'a militias have been playing the key role in the fight against ISIS. They were responsible for the first setbacks suffered by ISIS in the town of Amerli in Salah al-Din province. Ethnic cleansing of local Sunnis followed the "liberation" of the town. They have been crucial in subsequent engagements. The militias also played a key role in the recent victory against ISIS in Tikrit.

Palestinians

Among the Palestinians, Iran has been the sponsor of the Islamic Jihad movement since its emergence. Since the mid-1990s, Tehran was also engaged in constructing a strategic relationship with Hamas. Hamas bet on the wrong horse in the 2011-2013 period.

It assumed, as did many others, that a Muslim Brotherhood-led new regional alliance was coming into being, centered on Mohamed Morsi's Egypt and bankrolled by the Emirate of Qatar. Hamas saw itself as a natural member of this alliance. As part of its move toward it, the movement closed down its headquarters in Damascus and its activists relocated to Doha, Turkey or Cairo.

But, of course, the Brotherhood-led alliance proved a fleeting episode. The military coup in Egypt in July 2013 put paid to it. Since then, Hamas has been engaged in trying to rebuild its bridges to the Iranians.

Tehran has a natural interest in the sponsoring of Palestinian opposition to Israel. As non-Arabs and non-Sunnis, the Iranians are outsiders twice over in the largely Sunni, Arabic-speaking Middle East. Sponsorship of Palestinian "resistance" organizations is designed to contribute toward rectifying this outsider status – the Palestinian cause still being the great cause célèbre of the Sunni Arab world.

The latest evidence suggests that Iranian-Hamas rapprochement is proceeding apace. Tens of millions of dollars have been transferred to the Hamas-controlled Gaza Strip to help the movement re-arm and rebuild its damaged infrastructure. A new network of tunnels is under construction. Hamas really has no choice but to return to the Iranians if it wishes to continue its war against Israel.

Yemen

The toppling of dictator Ali Abdullah Saleh in 2011 paved the way for the growth of both Sunni and Shi'a militias in Yemen.

Lastly, in Yemen, Iran has long supported the Houthis. But the toppling of dictator Ali Abdullah Saleh in 2011 paved the way for the growing strength of both Sunni and Shi'a militias in the country. Iranian support for the Houthis has been constant, but has become far more overt since the movement took Sana'a in January.

The Houthis, in February, signed a civil aviation agreement with Tehran for direct flights between Sana'a and the Iranian capital, which will make the process of supplying Iran's allies in Yemen exponentially easier. In addition, an Iranian ship unloaded 180 tons of weapons for the Houthis at the port of al-Saleef in March.

Resistance to Iran

Maj. Gen. Qasem Soleimani, the principal architect of Iran's support for proxies in Arab states

So, across the region, where state authority has effectively broken down, it has been the Iranians who have been gaining the upper hand.

Nevertheless, it would be simplistic to conclude that the Iranians have simply swept all before them and that they dominate Lebanon, Syria, Iraq and Yemen without serious competition. The Iranians are providing effective support to one side in a civil war in Syria, Iraq and Yemen. But in none of these countries have they destroyed all opposition to their clients.

In both Iraq and Syria, Sunni Arab and Kurdish elements remain in control of significant sections of the country and are in no imminent danger of losing these to the clients of the Iranians.

Similarly, among the Palestinians, Iran appears to be rebuilding its links to Hamas and, therefore, to the Islamist half of the Palestinian national movement. But the Ramallah Palestinian Authority is backed by Egypt, Jordan, the Gulf Arabs and the West. Its security forces are trained in Jordan under professional Western supervision. It is in no danger of ceding ground to Hamas at any time in the future.

In Gaza, the Cairo government's closing of the tunnels to Sinai is leaving the Hamas enclave impoverished, forlorn and isolated. So, while the Iranians have an entrée to the Palestinian national movement, their clients are not within sight of defeating their enemies and are at the moment in a somewhat beleaguered position.

Even in Lebanon, where Hezbollah is without doubt the single dominant actor in a military sense, the movement does not exercise open, exclusive rule. And, were it to attempt to do so, the likely result would be to plunge the country into civil war.

Rather, Hezbollah maintains a parallel state structure created and financed by the Iranians. This structure acts without consulting the organs of the "official" state, sometimes in cooperation with them and sometimes in defiance of their wishes. But it does not seek to openly and entirely supplant the state.

So the Iranians are embarked on an attempt at regional hegemony. The effective creation and mobilization of local proxy political-military organizations constitutes a central part of this project.

Iran's ability to mobilize its proxies toward unified goals, and its skill in creating and training proxy political-military groups, has brought it considerable achievements in a variety of conflict arenas – but not yet total victory in any of them.

A Sunni coalition that seeks to challenge the Iranian advance toward regional domination is now in the process of being established. Saudi Arabia stands at the head of this effort.

The current Saudi-led Sunni mobilization against an attempt by an Iranian proxy to conquer southern Yemen has been the precipitating factor in galvanizing this Sunni response. It has an importance far beyond the narrow reaches of Yemen and represents the next stage in a process that began with the military coup in Egypt on July 3, 2013. That process is the emergence of a Riyadh-Cairo axis as the central element in current Sunni Arab diplomacy, in opposition to the mainly Shi'a alliance led by Iran.

Three factors contributed to the emergence of this axis. The first is the apparent abdication of the US from its role as the guarantor of regional security and the leader of the most powerful group of states in the Middle East. The second is the advance across the Middle East of Iran and its allies. The third is the challenge to status quo Sunni powers posed by Sunni political Islam in both its Muslim Brotherhood and Salafi forms.

The successful brokering by Saudi King Salman bin Abdulaziz al Saud of a united Sunni response follows the push by the Iran-supported Ansar Allah militia (popularly known as the Houthis) toward the city of Aden and the strategically crucial Bab al-Mandeb straits. This move to unite Yemen under their control is the natural next move for the Houthis and their Iranian backers following their capture of the Yemeni capital, Sana'a.

For the Saudis and their allies, this was a step too far. Yemen shares a 1,500 km poorly guarded border with Saudi Arabia.

Control by an Iranian proxy of this border would afford Tehran an additional means of direct pressure on the Saudis. Nine other Sunni states (Morocco, Egypt, Jordan, Sudan, Pakistan, Qatar, Kuwait, Bahrain, and United Arab Emirates) joined the desert kingdom in committing to prevent the further advance of the Houthis.

Until recently, Sunni attempts to hold back the Iranians and their allies appeared piecemeal and uncoordinated.

So what explains this sudden apparent success of Saudi diplomacy after a long period in which Sunni attempts to hold back the Iranians and their allies appeared piecemeal and uncoordinated? Is the new united Sunni response likely to hold? What results is it likely to achieve? And what might all this mean for Israel? It is strongly felt in Riyadh and other Sunni Arab capitals that the US is determined to withdraw from active involvement in the region and in pursuit of this goal is currently pursuing a dangerous path of appeasement of Iran. This is most notable, of course, in the nuclear negotiations, where Washington now appears to be willing to countenance Iran becoming a "threshold" nuclear power.

But this impression also derives from the US response to Iran's activities across the region. In Iraq, the US appears to be acting in tandem with Iranian goals, with no apparent awareness of the problems in this regard. In Lebanon, similarly, the West is supporting and equipping the Lebanese Armed Forces without understanding that the Lebanese state is largely a shell within which Hezbollah is the living and directing force. In Syria, the US is pursuing a half-hearted campaign against ISIS, while leaving the rest of the country to its internal dynamics.

From the perspective of the Saudis, Iranian ruthlessness, clarity and advance combined with the flailing, retreating US policy spells potential disaster.

A full-fledged Sunni alliance against the Iranians is emerging for the first time, independently of the US.

As a result, a full-fledged Sunni alliance against the Iranians is emerging for the first time, independently of the US. The resulting prospect is for a long Sunni-Shi'a conflict in the region to come.

What will be the implications of the current nuclear diplomacy between the West and Iran for the emergent Sunni-Shi'a conflict? Even under the impact of sanctions imposed because of its nuclear activities, Iran nevertheless managed to support its clients and allies. As stated above, it has continued to supply around $1 billion per month to the Assad regime in Syria and has continued to support Hezbollah, its clients in Iraq, and Hamas and Islamic Jihad among the Palestinians. In a pattern familiar to the experience of totalitarian regimes under sanctions in the past, Iran has preferred to safeguard monies for use in service of its regional ambitions while allowing its non-regime connected population to suffer the consequent shortages.

Nevertheless, with increased commitments in recent months deriving from the collapse of regimes in the Middle East, many observers have had a sense of looming Iranian "overstretch." Iran is now committed to supporting its allies and/or engaging directly in active wars in three Middle East countries – Syria, Iraq and Yemen. It is also heavily committed to supporting its clients in two other fraught arenas – Lebanon and Israel/the Palestinian territories.

Hezbollah in Lebanon has recently closed down a number of projects, such as the English-language website of the al-Akhbar newspaper. It has, according to a recent article in the Now Lebanon website, also reduced salaries to employees, stipends to political allies and wage payments to relatives of wounded fighters.

All these are indications of financial distress, as its patron Iran seeks to support an ever widening list of regional commitments.

However, should sanctions be substantially lifted in the months ahead, this would allow the freeing up of billions of dollars. It may be assumed that a considerable part of the funds freed will be put into the service of Iranian regional ambitions.

The emerging strategic picture in the Middle East is defined by the coming together of a number of factors.

The collapse of authoritarian regimes has resulted in the opening up of chaotic political spaces as would-be successors do battle over the ruins. These successor entities, in Yemen, Syria, Iraq, Libya, Lebanon and Gaza are usually based on local ethnic, tribal and sectarian identities. In the absence of a firm and crystallized national identity in these areas, these more primordial identifications have come to the fore.

The Iranian ambition for hegemony in the Middle East underlies Tehran's attempt to benefit from the burgeoning regional chaos. Iran controls a tight, centralized alliance of client organizations. Its clients control Lebanon and play a dominant role in Yemen, Iraq, Syria and Gaza.

The Sunni reaction derives precisely from the fear of a rampant Iran inheriting the regional order. The Sunni interest is preventing overall Iranian victory in Yemen, Syria and Iraq, but is not sufficiently strong to entirely defeat or push back the clients of Iran.

Lastly, the absence of the US from this picture is significant. Washington is working according to an erroneous reading of the regional map. It imagines that Tehran is amenable to "engagement." The result of this is to encourage Iranian expansionism and also to encourage the independent Sunni deployment to resist Iran that is now underway.

So the direction of events in the Middle East is toward an ongoing conflict on several fronts between a bloc of mainly Shi'a forces led by Iran and a looser, more disparate gathering of Sunni forces in which Saudi Arabia (and probably also Turkey and Qatar) are set to play central roles.

This conflict is set to define the next chapter of the troubled history of our region.

Jonathan Spyer is Director of the Rubin Center for Research in International Affairs and a fellow at the Middle East Forum. He is the author of The Transforming Fire: The Rise of the Israel-Islamist Conflict (Continuum, 2011).