The balance of diplomatic advantage between the foreign powers involved in the Syria conflict will inevitably reflect the momentum of the military situation. In that sense, as discussed in part 1 of this series, the Russians and Assad are in a far stronger position than their opponents.

Images of human suffering and refugee movements will continue to drive demand for diplomatic efforts to end the war. But unless, against the odds, the military situation changes to the marked disadvantage of Assad, the diplomatic process will remain focused primarily on securing humanitarian relief and supporting local cessations of hostilities. Some population transfers and negotiated surrenders are likely in regime-encircled areas.

This does not mean Damascus and Moscow will remain on the same page indefinitely. For Assad, meaningful power sharing with the Saudi and Turkish-backed opposition is unthinkable. But for wider geo-political reasons, the Russians (and possibly the Iranians) have an interest in seeing the conflict wound down in the medium term, on their conditions, of course.

Indeed, in terms of maintaining leverage over the regime, a negotiated settlement of the conflict, even if it were conceivable, may have less appeal in Moscow and Tehran than a series of de facto deals that leaves the Assad regime strengthened sufficiently to carry the main burden of its own defence but still requiring their assistance in facing an insurgency. With such leverage, Russia could continue to wage campaigns against potential threats to Russian security in Syria (notably the Chechen jihadists), and Iran could continue to use Syria as a base for its support of Hezbollah in Lebanon, which acts as a strategic counterweight to Israel.

In contrast to the Russians, the US has to build a negotiating process in conjunction with its military campaign against ISIS, one directed toward the haziest of political objectives for the future political character of Syria. It must do so while finding a workable balance between the competing demands of Turkey and the Kurds, the Syrian regime, as well as the Iranians and Saudis.

To avoid a further regional conflagration, at some stage Washington also needs to constrain, if not deny outright, the ambition for statehood of the Kurds, who will have contributed significantly to the military effort against ISIS. This will require Washington to deal constructively with Moscow, not least because the Kurds may threaten to draw closer to Russia to counter such policy thinking in Washington.

In the immediate future, the US won't be constrained by demands for a ceasefire as a precondition to negotiations. Far from representing an insurmountable bar to negotiations, the imbalance of the military situation makes it unlikely that the more vulnerable rebels, at least, can afford not to negotiate. If some progress is made at the bargaining table, the dynamics of the process may gradually bring others in.

Meanwhile, whether the US will countenance requests for additional military assistance to rebel groups depends on how the US sees the realities on the ground developing, as well as the dictates of diplomacy and coalition-building. But no US or Western interest would be served by jihadist groups such as Ahrar al-Sham, Jaish al-Islam and others spawned by al Qaida securing a role in Syria's future.

Unless a political earthquake rocks Washington, one thing will not change: US interests in Syria are not sufficiently important to warrant significantly deeper US military involvement.

US interests, including efforts to end the extraordinary suffering of ordinary Syrians, will be best served by seeking a regional political solution in conjunction with its military effort. The US will make the best of working with the Moscow and Tehran toward an outcome in western Syria. That outcome will be shaped militarily by the Russians and Iranians, but so far as the wider conflict and regional outlook is concerned, US diplomacy and military force will continue to play a vital part.

Photo courtesy of Getty/Andrew Reneissen.