It remains one of the most influential books of the century. Even its publicist, had it had one, could not have said that it races along, but it is a compelling work because it poses the uncomfortable question of what it means to be part of the West.
A new and intriguing assessment of our civilisation's prospects, Twilight of the West by Christopher Coker of the London School of Economics, confirms that I am not alone in catching echoes of Spengler in the millennial air. Spengler saw the West fading because it no longer believed in the values on which its own success was built. Cultures bloomed, then withered. Their souls succumbed to "metaphysical exhaustion", their body politic acquired "the heavy weariness of the thin and the old". Similarly Coker believes that we are facing the effective end of the Western Alliance, and with it the death of the West as the resort of collective ideals, aims and values.
It is strange that the fate of the West as a spiritual and intellectual force does not command much of our attention. "The West" is a term so familiar in our vocabulary, so reassuringly confident-sounding that we scarcely seem to have noticed that its meaning has shifted since "the East" stopped referring most commonly to the red bits on the map of the world and started meaning the emerging markets and economies of Asia.
I realise that the phrase "Western values" sounds pious. But the very fact that it does indicates a seepage of belief away from any common understanding of how the ideals of the Enlightenment should be represented in the way governments act. It is one of the great, arrogant misconceptions that changes as deep as that which occurred in 1989 in Europe unsettle only the peoples whose regimes fall or who retreat from positions of regional power.
The position of the victors has its own difficulties. Compare the callow certainty of Lord Ismay's description of Nato's purpose - "keep the Russians out, the Americans in and the Germans down" (it is impossible to imagine this mission-statement being delivered without the rap of a blackboard pointer) - with the bewildering multiple-choices the West now faces in setting priorities. The superpower conflict looks like a far more comfortable place to be.
Without it, the ties that link Europe to America have frayed. There are still Atlantist conferences at which Baroness Thatcher and Henry Kissinger appear like ghostly iridescences to bemoan the new, disordered world. But these occasions have the melancholy air of a nostalgics' reunion.
Is the idea of a particular bond between Europe and America one whose time has gone? Neither party has put much effort into keeping it alive. I looked up "Atlanticism" in a database of the Washington Post, and the word has appeared only 10 times since 1989, when George Bush announced the birth of the "New Atlanticism". The final mention was in 1995. If America has given up on the idea, its chances do not seem robust.
One response to this is to put all our eggs in the European basket. It must be nice to be a true European federalist, to believe that the model of integration we have on offer at present will lead to a stable and peaceful continent, which can say thank you and goodbye to Uncle Sam.
But I find it hard to believe that this will happen - or at least not for a very long time and not on the institutional foundations we have now. Many rhetorical "common European homes" have been promised since the collapse of the Berlin Wall, but they provided no shelter to the people of Vukovar or Srebrenica, let alone battered Kurdistan. Albania descended into bloody chaos, not least as a result of Western complicity in excusing electoral malpractice on the grounds that the alternative was worse. We undermined the very democracy we claimed to be promoting.
So a self-sufficient Europe is not on offer. There is little sign that, as a continent, we are anywhere near developing a common sense of purpose which transcends the selfish interests of the most powerful countries. A fraction of the political effort that goes into producing a common currency is devoted to expanding the EU to embrace the new democracies.
Most of all, it disturbs me that there is so little interest in the future shape and role of the Western Alliance on the European left - and still less in New Labour, despite the honourable, if neglected, tradition of Atlanticism represented by Hugh Gaitskell and Ernest Bevin.
Those left-liberal voices speaking most eloquently and persistently of the need to uphold Enlightenment values are heard in the emerging democracies of Eastern Europe. Last year I heard Vaclav Havel speak on what the West had meant to him during his life and what he wanted it to mean in the future. Lasting co-operation could exist, he said, only between countries "that have a strong idea of their own identity and values and the will to defend them".
That assumes we are aware of our interests and values, let alone being prepared to act on them. But Western Europeans are more cynical than ever before about American motives. The present threat of military action against Saddam Hussein is distrusted, not because its success is uncertain, but because it is interpreted as a cynical attempt to distract attention from President Clinton's carnal entanglements.
On this one, I give Bill Clinton the benefit of the doubt. His foreign policy is often made on the hoof. But that does not mean it is wrong. He has often done the right thing for the wrong reason. US intervention in Bosnia was belated, but it worked and will continue to do so as long as Congress screws its courage to the sticking place and keeps troops in place.
It was Mr Clinton who began the process of bringing the first wave of Eastern European members into Nato, despite the wailing of Cassandras who claimed that this would antagonise Moscow. It is Washington and not Bonn or London that fiercely upbraided President Milosevic when he interfered with the first free election this month in Montenegro.
It's strange and a bit disconcerting: I find myself admiring Mr Clinton more as a president at the very time that he is looking decidedly shabby as a human being. His foreign-policy record might be uneven, but it is better than anything Europe has offered so far in terms of determination and leadership in the wake of the Cold War.
Mr Havel has spoken, too, of a Europe that does not become an economic fortress, dedicated to the pursuit of its own prosperity, but of a continent which looks for common ground with other democracies and joins them "in the search for the common moral minimum necessary to guide us".
It is uplifting to hear it said so unambiguously that there are ways of life worth defending and that the West has a continuing, moral responsibility to do so. The fake allure of post-modernism does not render all choices equal, all ways of governing equally right. Values sustain us. That is what still provides a bridge across the Atlantic. For all our differences, misunderstandings and irritations, I don't want to lose it.