The interim deal between six leading world powers and Iran over its nuclear programme, agreed in late-night talks last weekend, could – if it bears fruit in the long term – transform the wider region; it could redraw the map of an area that has been gripped by conflict or the threat of conflict for generations.
In the midst of a growing schism between Shia and Sunni Muslims in the Middle East, fuelled by the war in Syria, an agreement that reduces the threat of an Israeli attack on Iran's nuclear facilities, sanctioned by the US, presents enormous possibilities as well as potential threats.
The first and most obvious benefit of the deal, ignored by Israel's hawkish prime minister, Binyamin Netanyahu, his allies in the US Congress and Saudi Arabia, is that the diplomacy that led to the interim six-month agreement is the first indication that under the new president, Hassan Rouhani, Tehran's clerical regime might now see the benefit of negotiating solutions to the region's problems, rather than its previous angry posturing under former president Mahmoud Ahmadinejad.
It is conceivable that such a shift might, at some point in the future, involve Tehran reconsidering its support for the Syrian regime of Bashar al-Assad and Hezbollah.
An Iran a step further back from conflict with Israel, and potentially minded to meddle less in the region, would be a good thing if Tehran sticks to its part of the deal: to dilute its stockpile of uranium enriched to 20% so that it is returned to 5% enriched, and not go ahead with the commissioning of the Arak reactor, which is able to produce plutonium.
But the deal creates new tensions as well in a Middle East already challenged by the upheavals of the 2011 Arab spring. Washington's decision to sideline its allies Israel and Saudi Arabia in the secret bilateral negotiations with Iran that began in August is in some respects as significant for the future as the nuclear deal.
Specifically for Israel, it can be seen as a rebuke to Netanyahu's long and vociferous insistence that Iran and its nuclear programme be treated by the US as an "existential threat".
It also marks a significant reshaping of the relationship with Sunni Saudi Arabia and the Gulf states. Riyadh not only fears the influence of a resurgent Iran – with which it is increasingly engaged in a proxy sectarian conflict in Syria – but is furious at what it sees as Washington's betrayal.
Turkey and Egypt, too, have been discomfited by the prospect that a deal might allow the emergence of Shia Iran – in alliance with Shia-dominated Iraq – as a significant regional power.
It is how these existing rivalries over the Iranian deal fit into the region's widening fracture lines that will define the future of the Middle East.
Relations between Turkey and Iran have been worsening in recent years, not least since Turkey agreed in 2011 to house a Nato radar base and as a consequence of the war in Syria, where Ankara has helped the Sunni rebels. However, energy-poor Turkey has been hard hit economically by the sanctions regime imposed against Iran. But the deal in Geneva appears to have given fresh impetus to efforts to thaw relations between Sunni majority Turkey and Tehran, with the Iranian president scheduled to visit Turkey in December. A thaw in relations between Ankara and Tehran could have positive consequences for efforts to find a peaceful settlement to the war in Syria.
Syria and Lebanon
The interim deal on Iran is a double-edged sword for Syria and Lebanon, which in different ways have both seen the fallout of the increased religious tension stoked by the war in Syria and by competition between Saudi and the Gulf states on one side and Iran on the other. On the plus side is the notion that if Iran holds to its side of the nuclear bargain it might persuade the international community to give Tehran a role in a Syrian peace process that could bring that conflict to an end. More likely, in the short term, is that friction between the parties will continue to be played out in proxy confrontations both in Syria, where Iranian Lebanese client group Hezbollah is openly fighting on the Assad side, and in Lebanon itself.
Israel and the peace process
The anger of prime minister Binyamin Netanyahu and his allies both in Israel and the US Congress over the deal – which they have compared to the Munich agreement that appeased Nazi Germany – marks a significant foreign policy defeat for Netanyahu and Israel. A potential casualty of the deal, in a context of the already difficult relationship between Obama and Netanyahu, could be the renewed US efforts to kickstart the Israel-Palestinian peace process – an area in which Netanyahu has long shown himself reluctant to make any meaningful movement.
Sunni and Shia divide
Fuelled in part by the conflict in Syria, the upheavals in the region since the Arab spring have seen growing tension and violence along the fault lines of the Sunni-Shia divide, not least in Shia majority Iraq which has seen sectarian violence growing month by month in the last year. In Bahrain and Lebanon sectarian tensions have also been rising.
America and the Middle East
After the long military engagement in Iraq, US participation in the fall of Libya's Muammar Gaddafi and accusations of a muddled and uncertain response to events in both Egypt and Syria, the interim deal is the first real suggestion that President Barack Obama intends to make a mark on the foreign policy front in the Middle East. Having spoken early in his presidency of his preparedness to speak to America's enemies, the tentative breakthrough with Iran – not least in the face of opposition by Israel and Saudi Arabia – suggests a willingness to take risks that has long been absent.
Saudi Arabia and the Gulf
Saudi-US relations have been frayed for some time. Points of friction have included Saudi's irritation over the US attitude towards the Muslim Brotherhood – which it detests – when the Brotherhood was in power in Egypt, and over its fears that any deal with Iran might lead to the resurgence of the world's most important Shia state. Since the advent of the Arab spring, Saudi Arabia has positioned itself aggressively in the worsening Shia-Sunni sectarian divide, helping to prop up minority Sunni rule in Bahrain and backing Sunni jihadis fighting in Syria against the Assad regime.
The interim six-month deal envisages sanctions relief to Iran to the tune of $7bn, opening the way for a long-term deal worth exponentially more. The hope of the Obama administration is that by demonstrating that there are solid economic rewards for Iran in co-operating with international demands over its nuclear programme, it will cement the more moderate government of Hassan Rouhani (above) after the rejection by voters of the policies of President Mahmoud Ahmadinejad. Iranian negotiators have warned, however, that because of continuing competition among hardliners and more moderate strands in Iranian politics hardliners could be resurgent without noticeable benefits to Iran. A fuller international engagement with Iran is also seen by many observers as a prerequisite to negotiating an end to the conflict in Syria. Tehran supports the Assad regime, concerned – for its own part – over what it sees as the emergence of an increasingly Sunni jihadist influence over those fighting the regime, backed by individuals in rival Saudi Arabia and the Gulf.