A rejection of failed foreign policy.
Iran has without doubt surrendered the most to reach this point. The conditions of the deal that will eventually lead to the lifting of the sanctions are onerous: only once the IAEA has verified that the country has taken a number of what were previously regarded as humiliating impositions on its right to nuclear energy will anything change. It's also likely the relief will be slow in coming should the conditions be met. The deal additionally maintains the ban on trade in conventional weapons for 5 years after sanctions have been lifted, 7 for that in ballistic missiles. For the west, the thaw in relations with Iran has been apparent for some time, and so the switch from the ridiculous maintaining of the country as one of the biggest threats to one of detached engagement, if not friendship, will not be quite as much of a shock.
The same cannot be said for Israel, where the reaction from those whose policies have only made the US more determined to reach a deal has been as over-the-top as expected. Last week Binyamin Netanyahu claimed Iran was both 100 times more dangerous than Islamic State, and like IS, was plotting to take over the world. Netanyahu's obstinacy and treatment of the Obama administration as though it's subordinate to him rather than other way around has seen only to isolate the country, leaving MPs to appeal desperately to Republicans to block the deal. Even if the Republicans vote en masse against the deal in Congress, with 12 right-wing Democrats joining them, Obama has promised to veto any legislation that prevents it being implemented.
Reaction has also been muted thus far from the Gulf Arab states, Saudi Arabia previously having lobbied the Americans to attack Iran. They can hardly fail to notice that at the same time as an alliance of Gulf Co-operation Council countries are attacking the Houthi rebels in Yemen, rebels they charge are funded by Iran, and as the proxy war in Syria continues to grind on, the Americans have pursued a policy entirely contrary to their usual allies' interests. Saudi threats of pushing ahead with the development of their own bomb are likely to be just that, threats. It does nevertheless signify the breaking of the status quo that has existed since the overthrow of the Shah: Iran has been brought in from the cold.
This doesn't of course mean the re-opening of the American embassy in Tehran is going to happen any time soon. Expecting a flip in allegiances, even if the deal is fully implemented, just isn't going to happen. The deal will though be intolerably wasteful if it results only in Iran not pursuing a nuclear weapons programme and the lifting of sanctions. Iran has long posed not a threat but an opportunity, if only our leaders had been willing to take it: a young country with a population that is far more outward looking than its neighbours, and in turn far more likely to embrace reform as long as it is respected rather than insulted and bullied. Bullying, meanwhile, is one of the few acts the Saudis have in their repertoire: in the recent past indirectly threatening this country lest their corruption be exposed or their demands for the banning of groups not acquiesced to. Their worldwide espousal of Wahhabism is one of the major factors behind the rise in international jihadism, while Iran is helping in the fight against Islamic State in both Iraq and Syria.
Hoping today's deal marks a watershed, a step change in the way policy is conducted in the region is almost certainly wishful thinking. It is though a rejection of the unthinking belligerence that defined the post 9/11 years, the cretinous bombing it better approach that has only made the Middle East more unstable and more dangerous. There will without doubt be a backlash, and it might not survive whoever becomes the next US president, whether Hillary or an as yet unknown Republican. All the more reason to entrench the agreement now, and push incrementally for a complete normalisation of relations with Iran. For a president often accused of achieving little, a legacy of health care, the beginning of the end of the embargo on Cuba, and a deal to end Iran's nuclear programme looks to these eyes from across the Atlantic as not a bad 8 years' work.