It wouldn't have happened six months ago. However, there have been some MAJOR shifts in international politics that require the Iranians to step back from the brink.

First (and foremost), the Iranian regime has been de-legitimised at home. Further sanctions would hurt the economy and destabilise an already unstable domestic situation. On the contrary, if the regime is able to improve the economy and see existing US sanctions lifted, it will be a major boost for Ahmadinejad at home. He can defuse much of the criticism he faced during the protests and perhaps reconcile factions within the government. Additionally, he could likely let up on some of the more odious elements of his "moral enforcement" of ultra-conservative principles.

Second, the United States foreign policy has made remarkable progress since the George W. Bush "if you don't agree with us we just might bomb you" aggressive stance toward the rest of the world. While in some quarters this policy may have seemed TOO friendly and conciliatory, it has reaped benefits. The European powers that counselled against an attack on Iraq are now acting hawkish toward Iran because we had said that, without a credible threat to the regime, the Iranians had no reason to negotiate. Now they understand - and precisely because we stepped back and said, "If you think you can do this better, go ahead and try." Of course, it also helps that more right-center politicians are now in charge of both of those countries.

Not only have we convinced our traditional European allies that a harder line needs to be taken, but we've convinced the Russians as well. We did this through a combination of ceasing activity that intentionally antagonised and provoked Russia and showing that we want to cooperate when possible, as well as through bluntly showing them the evidence that Iran had lied to everyone about its programme.