That chilly day in December is etched in Anatoly Yankovoi's memory -- thousands of angry young Kazakhs faced police cordons rimming Brezhnev Square in the centre of what was then the capital of Soviet Kazakhstan.

We were told they were drunken hooligans, but that was the beginning of the end. The end of the Soviet Union, says the retired police lieutenant-colonel, choking up at the memory. My heart is still aching, and the pain doesn't go away.

The bloody disturbances in Almaty in 1986 -- sparked by Moscow's summary dismissal of veteran Kazakh Communist Party boss Dinmukhamed Kunayev -- sent shockwaves across what had seemed an impregnable nuclear superpower, and led ultimately to the demise of the Soviet Union five years later.

The Commonwealth of Independent States was set up in haste by 11 of the 15 ex-Soviet states just days before Mikhail Gorbachev resigned as president of the Soviet Union on December 25, 1991.

From the outset, the loose grouping of impoverished new states was riven by separatism, ethnic conflict and economic disputes, raising questions about what they could possibly have in common.

Twenty years on, one thing they share is a nostalgia for the old Soviet days.

The Soviet Union gave me a first-class education, for which I did not pay, says Saijon Artykov, a 67-year-old retired geologist who supplements his monthly pension of $32 by selling potatoes in a market in Tajikistan's capital Dushanbe.

We did a lot of good in our time, discovering bauxite and gold deposits. We had good wages and I bought an apartment in Dushanbe, said Artykov, a graduate of the elite Moscow Mining Institute. Now we struggle to win our daily bread to survive.

Tajikistan, a predominantly Muslim nation and now one of Asia's poorest countries, lived through a civil war from 1992 to 1997 when its Moscow-backed secular government clashed with the Islamist opposition. Tens of thousands were killed.

Gulnara Ashimova, the 46-year-old owner of a beauty parlour in Bishkek, capital of next-door Kyrgyzstan, recalls low -- though admittedly stable -- salaries in Soviet times and restrictions on trips abroad for ordinary citizens.

But living in a country where violent revolutions have overthrown two presidents in the last six years and where ethnic clashes killed hundreds in June 2010, she would gladly swap her relative prosperity for the Soviet friendship of peoples.

Maybe our wages weren't that good, and I hated the 'Iron Curtain' most of all, but there was stability. There were the brotherly republics nearby, and you felt the shoulder of your neighbour, Ashimova said.

Hundreds of thousands of Kyrgyz and Tajiks now work abroad, mainly in increasingly xenophobic Russia, sending home the cash that props up the fragile economies of their home countries.

Kyrgyzstan's per capita gross domestic product of $843 is less than a tenth of that in neighbouring Kazakhstan, which has doubled oil production in the last decade on its way to becoming the second-largest economy in the CIS after Russia.

Financially, retired Kazakh policeman Yankovoi is much better off than Tajik pensioner Artykov. All the same, he too remembers the Soviet Union fondly.

We lost a great country, and I now have to cross state borders if I want to visit a friend elsewhere, he said.

BACK TO THE FUTURE?

Such widespread nostalgia is honey to the soul of Russian Prime Minister Vladimir Putin, who is preparing his return to the Kremlin next year.

Street protests in Moscow this week following an election which cut his party's majority in the lower house of parliament have toughened Putin's anti-Western rhetoric.

The man who once called the collapse of the Soviet Union the greatest geopolitical catastrophe of the 20th century reacted to the vote by accusing foreign countries of stirring up protests and trying to influence Russian elections.

Putin published an article in October outlining his plans to bring former Soviet states into a new Eurasian Union, saying that a stronger integration on a new political and economic basis and a new system of values is an imperative of our era.

Putin's idea has been embraced by Kazakh President Nursultan Nazarbayev, who has attracted more than $120 billion (76 billion pounds) in foreign investment since independence and presided over average economic growth of 8 percent annually over the last decade.

A similar proposal by Nazarbayev, a member of the last Communist Party politburo who some say had been poised to become Soviet prime minister, was quietly shelved in the 1990s after failing to grab the imagination of other CIS leaders.

Though Alexander Lukashenko, president of energy-strapped Belarus, joined his Russian and Kazakh counterparts in signing agreements last month to tighten economic integration, some analysts are doubtful that a wider Eurasian Union is feasible.

This is utopia. It will never happen, said Alexei Malashenko, analyst at the Moscow Carnegie Centre.

While Nazarbayev shares Putin's nostalgia and inherited a relatively industrialised nation with a large Slavic population, other former Soviet nations are suspicious of Moscow's motives and would be reluctant to join a Russia-dominated entity.

This is, in fact, a bilateral Russian-Kazakh union, said Malashenko. Whoever joins it will be driven only by abject poverty, hoping Russia will provide cash or cheap natural gas.

ENERGY AND PRIDE

There is no real incentive for Turkmenistan, Uzbekistan or Azerbaijan -- each with vast oil and gas resources, each with authoritarian leaders -- to enter a union with former imperial master Russia any time soon.

At various times during their independence, these emerging energy giants have infuriated Moscow by courting the West and China, securing billions of dollars in investment in return for promises of mineral riches.

National pride also stands in the way of closer integration. Ukraine, the most populous ex-Soviet republic after Russia, relies heavily on Russian energy supplies and its economy is now about 70 percent of its size before the Soviet Union collapsed.

But it has always treated with suspicion Russia's proposals to re-integrate the former Soviet republics within the CIS.

Being on the western and southern rim of Russia, Ukraine, Belarus, Georgia and Armenia would eventually like to integrate with the West, but also balance these close ties with Russia, said Lilit Gevorgyan, analyst at IHS Global Insight.

Russia's role in the various conflicts that have flared up on the fringes of the former Soviet Union is another key factor pushing some CIS members to reject a tighter union.

Latecomer Georgia joined the CIS in 1993, hoping membership of the Moscow-led grouping would help it resolve conflicts with the breakaway provinces of Abkhazia and South Ossetia lost to pro-Russian separatists in the early 1990s.

But the Caucasus nation abruptly left the CIS after it fought a five-day war with Russia in August 2008 after Georgia tried to re-establish by force its control over South Ossetia.

Moldova's two-decade dispute with pro-Russian separatists in its eastern Transdniestria region is also unresolved. Hundreds were killed when government forces clashed with the separatists in a brief but fierce war in 1992.

Late Russian Lieutenant General Alexander Lebed, whose paratroopers intervened to separate the warring sides in Moldova, is remembered in the CIS for saying: A person who does not regret the collapse of the Soviet Union has no heart. But the person who thinks it can be put together again has no brains.

CLUB OF INTERESTS

The CIS exists today as a loosely aligned club of interests within which members are free to choose their own paths. It's very inertia is what keeps it alive, Malashenko said.

Putin has said some ex-Soviet states made the wrong choice in turning away from Moscow to seek integration with the European Union, because in future the Eurasian Union would be the EU's partner in talks to create a common economic space.

It is hard to see how the CIS is going to compete with the well-developed European bloc driven by the shared vision of its members, said Gevorgyan of IHS Global Insight.

To win this competition, the CIS has to have a much more appealing ideology than that of the good memories and friendship of nations under the Soviet Union.

The ex-Soviet republics of Central Asia also have another ace up their sleeve: China lies directly across a common 2,800-km (1,740-mile) border.

Tatyana Zhdanova, vice-president of Kazakhstan's chamber of commerce and industry, says trade turnover between Kazakhstan and China has multiplied 200 times since independence. Chinese companies own nearly a quarter of Kazakhstan's oil production.

Official customs data show Kazakhstan earned $10.1 billion, or 17 percent of its total export revenues, selling goods to China last year, pushing Russia into third place after Italy.

Let's look at China as a strong partner that will in turn make us stronger, that will never let us sleep, said Zhdanova.

Chinese expansion, however, has inflamed passions within the former Soviet region, where opposition activists say governments are giving up too many precious resources and local residents bristle at the thought of any mass influx of Chinese workers.

Twenty years after the break-up of the Soviet Union, the migrant workers whose remittances contribute 40 percent of Tajikistan's GDP still flock mainly to Russia to join their Central Asian colleagues doing the menial jobs that help to keep Russia's $1.5 trillion economy ticking over.

The countries may have little in common but their shared Soviet past. But old habits die hard.

(Additional reporting by Roman Kozhevnikov in Dushanbe and Olga Dzyubenko in Bishkek; Editing by Robin Paxton and Sonya Hepinstall)