The nuclear agreement signed yesterday between Iran and the five permanent members of the UN Security Council plus Germany and the EU is a landmark piece of diplomacy. It promises to end Iran's prolonged isolation and could transform the conflict-ridden Middle East region by endorsing diplomatic engagement and possibly by realigning existing adversaries.
For President Barack Obama and President Hassan Rouhani in particular it signals the easing of a long, damaging confrontation between the US and Iran since the Iranian revolution of 1979.
Iran is a strong regional power with a sophisticated culture, a vibrant civil society and a proud and ancient civilisation and history. That revolution rejected the dependence on the US and western powers developed under the shah’s rule since they installed him in a coup against a nationalist government in 1953.
Nationalism was reaffirmed in 1979 through a regime of Shia Muslim clerical rule. A dreadful war with Iraq in the 1980s was followed by a decade of western sanctions culminating in the 2003 US-led invasion of Iraq. The US occupation empowered Iraq’s Shias, facilitating the expansion of Iranian proxies in Lebanon, Gaza and Syria.
The US spurned a similar deal to this one in 2005. As a result Iran’s nuclear power programme was hugely accelerated and more severe economic and arms sanctions were applied to constrain it for fear of a regional nuclear arms race.
That historical background is key to evaluating yesterday's agreement. Iran is entitled to develop civil nuclear power and its programme can continue. But under the deal its stocks of centrifuges and enriched uranium, necessary to a weapons programme, are sharply reduced while nuclear plants will face rigorous inspections led by of the International Atomic Energy Agency.
Proven non-compliance would see economic sanctions reinstated. Curbs on conventional weapon sales to Iran will last for five years, and those on missiles, eight.
Realism should caution against too high expectations from the agreement in transforming the region. But Iranians stand to benefit rapidly from the lifting of sanctions and the deal is likely to reinforce Rouhani's position as a popular reforming leader. Externally, however, the rooted opposition of Saudi Arabia and Gulf states to Iran's regional influence will inhibit rapid realignments. Israel, too, is utterly opposed to this agreement in fear of Iran – an antagonism that spills over into pro-Israeli Republican opposition to Mr Obama's championing of the treaty in US politics.
He has enough support to override congressional opponents if necessary. And he has every reason to see that the energy released by a successfully implemented agreement with Iran can help unblock at least some of the Middle East conflicts before he leaves office.