The immediate effect of the Russian intervention was to foreclose the "collapse" option. Whatever else happened, Russian air power would be able to prevent the Islamist forces from winning a decisive victory over the government army that would bring them to the borders of Lebanon and Jordan (and possibly right across them).
But Russian planners had no wish to be committed to an endless, expensive military campaign in a stalemated war. They needed an "exit strategy", and they had one.
The Russian political strategy was to secure the Assad regime's hold on the more populous parts of Syria, cut the flow of arms and volunteers across the Turkish border to the rebel forces, and then split the alliance between the Islamist and non-Islamist rebels.
This was a direct challenge to the strategy of the American-led "coalition" that has been bombing the Islamists who rule the so-called Islamic State (but not the other Islamists in Syria) for the past two years.
The US strategy envisaged destroying both the Assad regime and Islamic State, and accomplishing both these objectives without the help of any ground troops except the Syrian Kurds.
It was more a fantasy than a strategy, and many people in the US State Department and the Pentagon were aware it would probably mean handing Syria over to the Islamists.
Those people were secretly grateful when Russia intervened to save the Syrian Government, and they managed to limit the American reaction to general statements of "concern" that the Russians were bombing the wrong targets.
"Wrong targets" or not, unstinting Russian air support for Assad's army won it time to regain its balance and push the rebel troops away from Syria's key cities.
In the past month, the Syrian army, in de facto alliance with the Syrian Kurds, has cut the rebel supply line from Turkey.
Only the last part of the Russian strategy remains to be accomplished: split the alliance between the Islamist rebels and the non-Islamists.
And that is best done by politics: negotiate a ceasefire between the regime and the non-Islamist rebels that excludes the Islamists. That game is now afoot, and the people whom the US Government calls "moderate" rebels are clearly willing to play.
They might as well, for the "moderates" have been whittled down to less than a fifth of the troops who are actually fighting the regime. All the rest of the rebel troops in Syria serve Islamic State or its equally extreme Islamist rivals, the Nusra Front and Ahrar al-Sham.
Since the "moderates" have accepted the truce not offered to the Islamists, the split in the rebel forces has now been accomplished.
And since the United States now officially accepts this new definition of the "good and bad" rebels, the final stage of the Russian strategy has been accomplished: the great powers are all on the same side.
If this temporary truce can be converted into a permanent ceasefire, then the only remaining fighting in Syria will be around the borders of Islamic State in the north and east, and around the territory controlled by the Nusra Front and its ally Ahrar al-Sham in the northwest.
If the US can swallow the bitter reality that this truce leaves the Assad regime in charge of the territory it now controls (and around two-thirds of the Syrian population), then the Syrian civil war could eventually be shrunk to a war of everybody else against the Islamists.
And along the way it would give the US and Russia a chance to rebuild a more co-operative relationship.
Gwynne Dyer is an independent journalist whose articles are published in 45 countries.
