George W. Bush is absolutely wrong in his support for Nato enlargement. That goes without saying. What is more surprising is that Vladimir Putin is absolutely right in both the conclusion and the reasoning behind his outspoken, even threatening, opposition to America on this issue. And that applies with even greater force to Dmitri Medvedev, the incoming Russian president, who has gone farther even than Mr Putin in suggesting that a decision by the West to entertain the membership applications presented by Ukraine and Georgia to the Nato Council would be tantamount to a declaration of cold war.

If a genuine spirit of peaceful co-operation is ever to be created between the West and Europe's most populous country - and what may one day be its biggest economy - then our leaders will have to think much more deeply about the legitimate grievances that Nato's enlargement arouses in Russia.

Ever since the dismemberment of the Soviet Union by Boris Yeltsin in 1991, the enlargement of Nato and the EU towards Russia's western and southern borders has looked like to Russians the last remaining expansionist empire in Europe, perhaps in the world.

While EU enlargement on its own could be presented as an economic enterprise, designed mainly to raise living standards in Central and Eastern Europe and even to increase the potential of Russia's neighbours as trading partners, the combination of the EU and Nato is a very different proposition.

EU-Nato, under the Bush doctrine of continuous eastward expansion, becomes an unstoppable politico-military juggernaut, advancing relentlessly towards Russia's borders and swallowing up all intervening countries, first into the EU's economic and political arrangements and then into the Nato military structure. Considered from the Russian standpoint, Nato's explicit new vocation to keep expanding until it embraces every “democratic” country in Europe and central Asia, with the unique and critical exception of Russia itself, becomes hard to distinguish from previous expansions into eastern territory by French and German heads of state whose intentions were less benign than those of the present Western leaders.

Western politicians may ridicule such fantasies as Russian nationalist paranoia. But why shouldn't the Russians worry about Western armies and missiles moving ever closer to their borders? This contributes to a territorial encirclement very similar to what Napoleon and Hitler failed to achieve by cruder means. The official Western answer is that Nato's expansion is purely defensive, that no Nato country would dream of claiming even an inch of Russian soil. But the feigned innocence of the West's baffled answer to the encirclement protests only intensifies Russia's sense of fear and provocation - and there are at least three reasons why the Russians are right to feel aggrieved.

Russia's first reason for justified resentment relates to the purely “defensive” nature of Nato's expansion. As President Putin put it in his notorious (to Westerners) or celebrated (to Russians) Munich speech last year: “Nato expansion does not have any relation with ensuring security in Europe. On the contrary, it represents a serious provocation that reduces the level of mutual trust. And we have the right to ask: against whom is this expansion intended?”

Given that Russia is the only country in Europe (or in central Asia) that has been explicitly barred from Nato - and that will remain barred as long as Poland and the Baltic states are members - the only possible enemy implied by the alliance's “defensive” posture must be Russia itself. Every defence policy statement from Central Europe makes perfectly clear that defence against Russia is the main raison d'être of Nato. And given the Polish and Baltic experience of Russian occupation and oppression, it is hardly surprising that they see Nato's mission in a different light from President Bush or Gordon Brown.

Moreover, the anti-Russian motivation for joining Nato is even clearer in the case of Ukraine and Georgia - and this is the second reason why the Russians are right to feel provoked. It may be argued that Ukraine and George are justified in being hostile because Russia has been meddling in their politics ever since they became independent in 1992. In the case of Georgia, this has extended to military support for separatist movements in Abkhazia and Ossetia. In Ukraine, Russia has backed politicians representing the large Russian-speaking minority and allegedly tried to fix elections or even kill politicians on their behalf.

Whatever the rights or wrongs of these allegations, the mutual hostility between Russia and Ukrainian and Georgian nationalists is an undeniable fact of life. If these countries became members of Nato, any Russian interference in their internal affairs would have to be regarded by other Nato members, including America and Britain, as a declaration of war. It is possible to imagine a Russian decision to arm separatists in Abkhazia triggering a latter-day Cuban missile crisis - with potentially devastating results. In this sense, Ukrainian and Georgian admission to Nato, even if it were morally justifiable on the basis of Western democratic values, must also be understood from the Russian standpoint as a hostile act.

But surely democracy must prevail in the West's decisions? Surely the rights of former Soviet states to national self-determination must be defended at all costs, even if this carries a remote risk of military confrontation? But is democracy and self-determination really what Nato membership for these countries would defend?

The main reason why both these countries, whose borders are arbitrary creations of Soviet times, are so eager to join Nato is that they both contain regions that wish to secede. Large numbers of ethnically Russian Ukrainians and Georgians would almost certainly want to rejoin Russia. In the case of Abkhazia and Ossetia, some of these people have gone so far as to start military secessionist movements. If Nato embraces Ukraine and Georgia to guarantee their democratic self-determination, what will be the answer if Russia demands a referendum on secession among the people of Abkhazia or Crimea?

The answer will not depend on morality but on power. Democratic self-determination has never been an inviolable principle of geopolitics - and for very good reasons. This argument is never used, for example, to suggest that Taiwan should be invited to join Nato. Indeed, Taiwan is not even diplomatically recognised by any Nato government, even though the people there have repeatedly voted for autonomy, while China has overtly threatened to retake the island by force.

Why, then should the West offer military guarantees against Russia to Georgia or Ukraine? The reason, of course, is that China is too powerful and important for Western governments to risk provoking, while Russia is perceived as weak and irrelevant.

That perception of weakness, is the third reason why the Russians are right to feel aggrieved - and why Nato should beware of pushing too far. Germany was weaker in the 1920s than Russia is today. But, history shows that weakness doesn't last for ever.

Times Recommends

• We have kit and leadership. Let’s go
• Behind the scenes at the biggest deal
• Conferences — what a waste of money