It was, in the words of its national anthem, a "union of free and indivisible republics". It lasted more than 70 years. It pioneered the exploration of outer space, and bored the world's deepest oil wells. It had a quarter of the world's scientific manpower, and headed a group of states that accounted for about a third of the world's population.
The Soviet people, in March 1991, overwhelmingly declared in favour of its retention as a "renewed federation". And yet, in December that year, the USSR passed into oblivion - or at least it seemed to have done.
Just a few years later, its collapse seems all but inevitable to a new generation of undergraduates. For a start, there were deep-seated divisions among the hundred or more nationalities. And among some, particularly in the Baltic, there were movements for full independence that attracted a mass following. Recognising the inevitable, the Soviet authorities conceded their independence late in 1991 - and the three Baltic republics rejoined the international community.
In any case, the USSR hardly seemed a going concern. National income fell by 17 per cent in 1990, more than the United States suffered during the Great Depression. Viewed from the Baltic, or indeed from most other republics, it was surely a better idea to develop their own solutions - particularly if they were rich in natural resources. Yet there was, in fact, nothing inevitable about the collapse of the USSR in 1991 - although it would clearly have had to change. When the Soviet people were invited to express a view, in the country's first referendum in March 1991, there was a turnout of 80 per cent; more than 76 per cent declared in favour of the maintenance of a "renewed federation" in which the human rights and freedoms of all nationalities would be "fully guaranteed".
As late as November 1991, three months after the coup that triggered Gorbachev's downfall, nine of the original 15 republics reached agreement on a new "union of sovereign states", with a single parliament and a directly elected presidency.
But the following month, on December 1, the Ukraine held a referendum on independence. It was supported by more than 90 per cent of those who voted, and there was no prospect from this point onwards that the second most important of the republics would take part in a new union. Yeltsin concluded that there was no point in further discussions, and on December 8 the leaders of the three Slavic republics, Russia, Ukraine and Belarus, founded the Commonwealth of Independent States - a body that was not a state but an intergovernmental organisation.
By the end of the year all that was left of the Soviet Union in a formal sense was a mass of postage stamps that still featured the hammer and sickle.
Or was it? After more than 70 years, there was a great deal more. For a start, it was under the same management.
Boris Yeltsin had been a Communist party member for more than 30 years, and a member of its Politburo. Indeed, there was a high level of continuity between the old nomenklatura and the new Russian elite: about three-quarters in the presidential administration, and over 80 per cent in the regions.
The economies, even after 1991, were still intertwined. More than half of all Soviet trade in the late 1980s was interrepublican, and trade between the republics accounted for about a quarter of gross domestic product. The collapse of this trade affected all the republics after 1991, and provided the strongest grounds for moving back towards a single "economic area" along the lines of the much-admired European Union.
The Soviet peoples themselves were intertwined. Nearly a fifth of all marriages were of mixed nationality by the late 1980s. And more and more lived outside their own republics - about 75 million, including 25 million Russians. Russians were nearly as numerous as Kazakhs in Kazakhstan, they were more than a third of the population of Latvia, and more than a fifth in the Ukraine and Kirgizia.
What, by the mid-1990s, did ordinary Russians make of it all? They were clear that the decision to dissolve the USSR had been a big mistake. According to the New Russia Barometer conducted for the centre for the study of public policy at the University of Strathclyde, only 12 per cent thought it had been the right decision; 68 per cent took the opposite view. And how, the NRB asked, had the collapse of the USSR affected their living standards? Just 4 per cent thought their living standards had improved; a massive 76 per cent thought the effect had been unfavourable.
There were different views about which former republics Russia should seek an association with if a USSR were to be reconstituted. Ordinary Russians, according to the NRB, were most in favour of a closer relationship with the other Slavic republics, Belarus (89 per cent in favour) and Ukraine (87 per cent in favour). Kazakhstan (74 per cent in favour) was also popular; but only a bare majority supported an association with the other Central Asian republics, and relatively few favoured an association with the Caucasian and Baltic states (just 39 per cent wanted a close union with Estonia, for instance).
A vox pop conducted by the popular weekly paper, Argumenty i fakty, echoed these findings earlier this year. The first person they asked, Yuri Zubitsky, temporarily out of work, was "for the USSR, however stupid that might sound".
Elena Tkalenkova, a businesswoman, was against - it could only mean the return of psychiatric prisons, lies and censorship. But Sergei from Moscow thought the "three Slavic brothers" were "simply fated to live together". And Boris, a down and out, had a simple explanation: "When there was a USSR, I had a flat. Now there is no USSR - and I've no flat either."
It seems unlikely, despite such support, that a USSR will ever be reconstituted in its original form. Elites in the newly independent republics have acquired a taste for freedom, and sometimes a stake in privatised property. And Russians themselves are reluctant to combine with other republics that they would have to subsidise.
But an association that stops short of reintegration has already begun to take place, most notably between Belarus and Russia. As Gorbachev put it, the state had gone but the "feeling of a single country is still alive". Under, let's say, a President Lebed, it could be back in business Stephen White is professor of politics at the University of Glasgow.