There's a nostalgic quality to the angry demonstrations that have greeted the arrival of the Olympic flame in Europe and the United States this week.

For some time now the modern wisdom that has brought young malcontents on to the streets of London, Paris and San Francisco has held the US and its dependable ally Britain to be the root of all evil. Governments from Beijing to Caracas could trample their citizens into the ground and you wouldn't fill a telephone box with people upset about it. But call for the heads of the warmongers Bush and Blair and a million pairs of brave feet would take to the streets to support you.

So it's a quaint departure for those same crowds, albeit in much smaller numbers, to protest loudly against the actions of men for whom tyranny is a chosen method of governing rather than a silly label attached by adolescent-brained politicians.

The mêlées this week actually have real historical resonance, an echo of the Cold War. They are a reminder of the days when the Olympics were a battlefield in the great ideological struggle of the time. The US-led boycott of Moscow in 1980 and the Soviet Union's retaliation in Los Angeles four years later were in the end no more than gestures, as meaningful as all the other Games of the era when the two superpowers fought for gold medals as keenly as they fought for the affections of Third World leaders.

The 2008 version of the battle is lower key but this little struggle is a mirror on the most important simple political fact of our times - the global struggle for supremacy between liberalism and its enemies.

When the Cold War ended, it was widely assumed to mark the glorious culmination of the steady march towards freedom that had characterised human history. This is an old temptation of historians: the belief - call it Hegelian or Whiggish - that some great unseen hand was moving humanity in a direction called progress.

For a while it looked right. Since 1974 90 countries have become free. By 2000 60 per cent of the world's people lived in democracies. Even holdouts against the tide seemed only to make the point. In the 1990s the persistence of communist rule in China was treated as the exception that was merely testing the rule. The Chinese leaders were on the wrong side of history. The economic liberalism they had embraced as a defensive mechanism would soon force a political revolution.

But for the past few years democracy has been in global retreat. Notwithstanding a small occasional triumph here and there, in Latin America, Africa and in Eastern Europe, the tide has been turned.

The most significant defeat of all has been in China, where the success of limited capitalism has not been matched by political freedom. Two decades on, and three times as rich as it was, China seems less susceptible to real change than it did when the students lit up Tiananmen Square in 1989. China's success is no longer seen as a temporary aberration, a sort of unsustainable balancing act that would sooner or later collapse. It is viewed increasingly by ambitious autocrats everywhere as an alternative model to the vexingly unpredictable Western version. Its biggest recruit is Vladimir Putin's Russia, which steadily tightens its grip on the reins of political power as its business leaders exploit the lucrative opportunities of free global markets.

As Robert Kagan, the neoconservative historian and occasional speechwriter for John McCain, argues persuasively in The New Republic, this is the defining historical struggle of the 21st century.

The stakes seem on the surface somewhat lower than they were in the Cold War, the threats less immediate. China watchers say that what drives Beijing's leaders above all is a determination to survive at the pinnacle of an unwieldy country whose size and diversity represents a constant challenge to its stability. Russia may be increasingly autocratic but it no longer points its missiles at us (we hope).

In many ways, it is the fact that this struggle seems less urgent to us that makes us less well placed to win it than we were in the Cold War. For one thing, despite our fears of Soviet communism, we were never in any sense economically dependent on what that failed system had to offer. Today China, with its vast store of US Treasury bonds has American prosperity in its grip. Russia, with its stranglehold on continental energy resources, can intimidate Europeans. That's why George Bush would never boycott the Beijing Olympics and why the Europeans, in a cringing genuflection to Russian “concerns”, recoiled energetically last week from proposals to expand Nato.

Meanwhile, the global struggle against Islamism weakens the resolve, resources and unity of the West, while Russia and China deflect jihadism's ambitions through useful accommodations with its practitioners in Iran, Syria and Palestine.

Above all, we in the democratic world, fattened by prosperity and complacent in the inevitability of the victory of our values, are more prone than ever to the corrosive luxury of self-questioning: the sort of domestic posturing that results in a mayor of London extolling the virtues of Fidel Castro or Hugo Chávez.

For liberalism to prevail it will not necessarily require open confrontation or military buildup, or even the empty gestures of Olympic boycotts. But it will require a good deal more willingness by the West to defend itself and its interests and to stand up for liberal democracy around the world rather more effectively and enthusiastically than of late.

We shouldn't forget that the outcomes of the struggles between liberal democracy and its enemies were no more predetermined in the 20th century - look at where we stood in 1940 or 1979 - than they are today. It was only thanks to the resilience of Western populations and brilliant statesmanship that our values triumphed then.

Who can be so confident, surveying the state of morale and leadership today, that such a triumph is inevitable in this century?

Times Recommends

• Bank charges hit us for being human
• Sorry, Father, thou still shalt not steal
• The shed where Santa’s failures go to die