Does Iran nuclear deal pave way for Syria compromise? Not so fast.

What allowed Iran and world powers to reach an agreement was avoiding matters where interests diverge -- like Syria.

There's been some speculation in the wake of an interim agreement between Iran, the US and others on the Islamic Republic's nuclear program that the thaw in relations could lead to progress on other matters of dispute, like the civil war in Syria.

Peace talks between the Syrian regime and rebels have been announced for Jan. 22 in Geneva, the same city that the nuclear talks were held in.

But the key to understanding progress on Iran's nuclear program is this: There was a middle ground available that allowed everybody to get something that they wanted. For Iran and its new centrist President Hassan Rouhani, who took office a little over three months ago with a pledge of more openness to the world and a stronger economy, there is relief from sanctions that have taken a huge bite out of the Iranian economy. For the US, there is a chance of reassurance that an Iranian nuclear bomb isn't looming, and at the cheap price of diplomacy, rather than the dear and uncertain one of war.

While it's far too soon to predict where US-Iran relations will be a few years from now, and whether this is really the first step towards the true detente that many are hoping for, this remains a relationship built on each nation's view of its own interests. And when it comes to Syria, the interests of the US and Iran could not be more divergent.

Syria's civil war has become a proxy for Iranian and Saudi rivalry in the region. The Saudis are eager for the secular-leaning regime of Bashar al-Assad, who belongs to the Alawite offshoot of Shiite Islam that the Saudi religious establishment views as an assault on the purity of Islam, to fall. They want Syria's next government to be dominated by Sunni Arabs that will at the very least tolerate the flow of money from Saudi donors to jihadi groups in Syria. The US has been tacitly backing Saudi Arabia's play (the Saudis are angry that the US isn't arming Syria's rebels, but the US is on board in public with the "Assad must go" position).

The Iranians, meanwhile, are sending money, guns, and military trainers to help Mr. Assad survive, since his government remains a rare friend in the Arab world and they fear a long-term hit to their regional interests if he falls.

In short, Iran would still see the defeat of Assad as a disaster that could have destabilizing consequences for its only other close Arab friend, Iraq. Saudi Arabia, and the US, meanwhile, would view Assad's survival as a disaster. That doesn't present much ground for compromise.

For the Syrians themselves, it's also hard to see how these planned so-called "Geneva II" talks (following "Geneva I" in the summer of 2012, which accomplished nothing) will change much. The rebels are not willing to compromise yet on Assad remaining in power. Assad is unwilling to go - and there are no signs that his regime is willing to jettison him in exchange for the survival of its core. And the "rebels" aren't really anything approaching a united group - not ideologically, not in terms of command and control, and certainly not in terms of visions for the future. The whole question of who will speak for the rebels at Geneva remains a minefield.

This has been the state of play for some time. I wrote in October of last year that United Nations Syria envoy Lakhdar Brahimi's musings about cease-fires and common ground leading to a negotiated settlement should not be taken seriously. I think that's still pretty much the case:

Brahimi is apparently telling reporters that he hopes a temporary cease-fire around the holiday, which starts on Oct. 24, will form the basis for a negotiated settlement to the war.

If he really believes that he will be sorely disappointed. There are simply no grounds for a negotiated settlement at this point. The rebels will not accept the survival of Assad's Alawite dominated Baathist regime, nor will the foreign sponsors in the Gulf of the increasingly well-armed Sunni Islamist component of the rebellion. Perhaps Brahimi is hoping that Assad and the regime hard core will use the cease-fire to negotiate their own arrests and seizure of their assets? Or perhaps the rebels, after so much bloodshed and threats from the government to lay wasted to their whole families, will decide that the current dictatorship really isn't so bad and pack it in?

Just as there isn't much common ground between Iran and the US on Syria - there isn't much common ground to be found between the rebels and the regime. At least not yet. Nations and groups will carry on pursuing their interests.

This has long been the way of things. If the current six-month nuclear agreement with Iran leads to a more durable breakthrough - one that sees Iran not hemmed in by sanctions, and countries like the US not afraid of possible nuclear proliferation - that will be thanks to focusing on areas of common interest and not the ones of inevitable dispute.