By Jonathan Marcus
BBC's diplomatic correspondent, Brussels
The crisis in Georgia has presented Nato with both an opportunity and a challenge.
Moscow insists its troops have begun pulling back, as promised
Here was a moment to prove the alliance's validity - indeed even its credibility - in a new security order that differs markedly from its formative years in the Cold War.
Nato has had to carry out a complex diplomatic balancing act: supporting Georgia while trying to contain its rhetoric within the bounds of the possible, and sanctioning Russia while not putting relations back into the deep freeze.
This is a mark not so much of Nato's relative weakness in this dispute - it does indeed have few levers with which to play - but it is more an acknowledgement that we live in a much more complex world where ties between Russia and the West have a number of dimensions - not least an energy relationship - and a freeze could hurt the Europeans more than it would hurt Russia.
For all the overtones from the past - Russian tank columns on the march evoking memories of Hungary and Czechoslovakia - this was a crisis with parallels more in the 19th Century than in the one that has recently ended.
This is not about an expansionist state with an ideology bent on world domination, but a major power eager to establish a sphere of interest in its own backyard and jealously guarding what it sees as the approaches towards its own frontiers - what Russians have traditionally called the "near abroad."
Nato, though, was intent on signalling some red lines of its own.
Condoleezza Rice denied that the US wanted to isolate Russia
Indeed lines were very much on the mind of US Secretary of State Condoleezza Rice who gave voice to the views of many when she noted that there could be no turning back of the clock in Europe.
"This alliance, having come so far after the end of the Cold War and the collapse of the Soviet Union in achieving a Europe that is whole, free and at peace," was not, she went on, "going to permit a new line to be drawn in Europe between those who were fortunate enough to make it into the trans-Atlantic structures and those who still aspire to those transatlantic structures."
In other words, Nato's doors will remain open to countries like Georgia and indeed Ukraine.
To underscore the parallel importance of these two countries to the alliance, Georgia is now to be offered a Nato-Georgia commission along the lines of a similar body linking the bloc and Kiev.
This - in Georgia's case - is largely a symbolic manifestation of the alliance's resolve.
But the message could not be clearer: these countries have a democratic choice to opt for the "trans-Atlantic" camp and Russia is not going to be allowed any veto over their ambitions.
There is going to be practical help for Georgia too: aid in rebuilding its shattered infrastructure, its air traffic control system and ultimately its military defences too.
So far then, Nato seems to have passed the Georgia part of this test. Everyone, of course, has conveniently forgotten that Georgia can never in practical terms be part of Nato until its territorial disputes with Abkhazia and South Ossetia are resolved.
Nato has never imported unfinished business into the alliance - certainly not unfinished business that threatens to turn into a military conflict with Russia.
So resolving the Abkhaz and South Ossetian disputes is essential if Georgia is ultimately to join Nato's ranks. And that, of course, requires engagement with Russia.
For now, though, Nato is making it clear that Russia's military adventure in Georgia has inevitably damaged its relations with Moscow.
Meetings of the Nato-Russia Council appear effectively to be frozen and the message from Nato headquarters again is clear: worse could follow if Russian troops do not get out of Georgia soon.
So tough words for Russia but in fairness little real action - the consensus view being summed up by Britain's Foreign Secretary David Miliband who called not for Russia's isolation but for, what he termed, hard-headed engagement with Moscow.
"We need," he told me, "to make absolutely plain to Russia the consequences of its actions, the consequences of its misadventures."
Mr Miliband said that he did not want to play to what he described as Russia's "penchant for victimhood".
"We must not make Russia the victims of this affair," he underlined. "They are actually the transgressors."
So has Nato passed the Russian element of this test? Here the verdict can only be an interim one.
Ossetian protesters held a protest rally outside Nato headquarters in Brussels
The allies are divided on how far to punish the Russians. Indeed there might have been greater division at this Nato meeting if Moscow had actually begun its troop withdrawal. As it was, Russia's inaction galvanised Nato unity. But for how long?
The real issues concerning Russia's relationship with the West fall into the medium and long term.
This has all been an object lesson for the aspiring US presidential candidates in the realities of old-style power politics.
Russia may indeed have a veto over Georgia's membership of the alliance. Not because of threats and bluster but simply because it may decide to hang on to Abkhazia and South Ossetia, disregarding Georgia's sovereignty.
What price then for Georgia's Nato aspirations?
A famous US academic characterised the end of the Cold War as "the end of history". Well, in the past two weeks we have seen the return of history with a vengeance.