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For decades, they were the untouchable monoliths of politics: The big nation-wide parties that straddled the centre ground, leaning slightly to the left or right, capturing big swathes of votes across the spectrum, forming the lion’s share of national governments during the half-dozen decades after the Second World War.

The Liberals in Canada. The Christian Democrats and Social Democrats in many European countries. Labour in Britain and the Netherlands, and the Socialists in Spain and France. These big-tent operations covered so much of the electoral horizon, and spent so much time in power, that they came to be known in many countries as the “natural governing party.”

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Suddenly, they are falling apart, their gradual seepage of voter support during the past 10 or 15 years exploding into sudden ballot embolisms. Canadians experienced the meltdown firsthand last month with the dramatic collapse of the Liberal party – in which fewer than one in five Canadians voted for a party that had dominated politics for a century, and its standing fell from 77 seats to 34 overnight, all but disappearing in Quebec and the west.

This was merely one event in a season of big-party cataclysms across the Western world. Like a row of wave-battered skyscrapers collapsing into the ocean, the world’s mighty centrists are being humbled by formerly fringe challengers from the left and the right. The big political party seems to be headed for extinction.

“We’ve seen a real hollowing-out of the mainstream parties,” says Olaf Cramme, director of the London-based European think tank Policy Network, which has recently completed a large-scale study of the factors that decimated Europe’s big centre-left parties in the last several years.

“It’s been a general decline on both sides – it affected the social democrats and liberals earlier than the centre-right, but the decline has hit the mainstream parties wherever you look,” he says.

Like dominoes

Only weeks before the Liberal collapse in Canada, Angela Merkel’s Christian Democrats, the conservative party that has governed Germany more often than not in the decades since the war, suffered its most humiliating defeat. In Baden-Württemberg, one of Germany’s most wealthy, populous and loyally conservative states, her party suffered a mammoth defeat at the hands of the previously marginal Green Party – closely following another shock defeat in Hamburg state elections, and a deep slide in national poll standings. It is not as if her traditional big-tent opponents, the Social Democrats, are doing better: They have suffered a deep fall in support, losing votes to the neo-communist Left Party, the Greens and other fringe voices.

And only days after the Liberals melted down, Britain’s already humbled Labour Party suffered a similar beating in Scotland, losing most of its traditional voter support to the separatist Scottish National Party, which won a majority. And their broad-spectrum opponents, the Conservatives, have been unable to govern Britain without the backing of the once-marginal Liberal Democrats – leading many pundits to say that Britain is unlikely to have a majority government again.

The meltdown continued this week: The arrest of French IMF chief and presidential hopeful Dominique Strauss-Kahn on sex-assault charges in New York City didn’t just strip the centre-left Socialist Party of its most viable candidate; it also revealed that the party’s support has badly fallen, that it lacks the talent pool to throw up any other inspiring candidates, and that it may well lose badly to more extreme parties. President Nicolas Sarkozy had little reason to gloat, though: His conservative UMP (Union for a Popular Movement) party, the descendent of the party founded by Charles de Gaulle and a permanent fixture on the French landscape, is at its lowest level in recent history, and polls all year have shown that the extreme right wing National Front, led by Marine Le Pen, is now the second most popular party in France, stealing a huge chunk of the formerly secure UMP vote. As with Silvio Berlusconi’s Italian coalition, many observers wonder if the UMP will exist as a big party after the 2012 election.

And so it has continued: In the Netherlands, the powerful Labour Party was emasculated and booted out of the governing coalition in this year’s elections. In Ireland, the twin centrist forces of the Fianna Fail and Fine Gael parties were chiselled down to stumps in this year’s election, with once-tiny parties gaining considerable ground.

This is a phenomenon across most of the Western world. According to the Parties and Elections in Europe database, the combined standing of the two largest parties in Britain, Germany, Austria and Ireland has fallen from 75 per cent of the vote in 2000 to barely 50 per cent today; other countries, like the Netherlands, have seen even steeper declines.

Before the meltdowns, the meltdown

The hemorrhage of centrist votes began in earnest with the financial crisis of 2008, when a surprising number of voters shifted away from the big all-in-one parties to “outsider” voices – single-issue parties such as the Greens and the anti-immigration parties of the Netherlands and Scandinavia, traditional parties of protest such as the NDP in Canada, anti-system parties such as the Scottish and Catalan separatists, or forces of indiscriminate anger, such as the right-wing National Front in France.

This is not so much a shift of voters to more extreme politics, Mr. Cramme and his colleagues concluded in their analysis of polling in a dozen countries, but rather a surprising but predictable response to the way the crisis unfolded: While it began, in 2008, as a private-sector crisis of bad debt and unsupported credit in the financial and banking sectors, this was quickly followed by bailouts and rescues that shifted the burden to the state. Private-sector debt and potential insolvency turned into public-sector debt and higher taxes to pay for it, and the parties in power got blamed.

In essence, the bailouts worked all too well. The banking, finance and insurance industries were rescued by the state, so voters never experienced anything that would have turned their rage against the private sector: runs on banks, disappearing mortgages, lost retirement savings.

Many voters’ first personal experience of the crisis was an announcement of a tax hike, massive government debt, or slashed public service being used to pay for the crisis; this, combined with a job loss and a fuel-price spike, turned people against the parties that oversaw the crisis.

On top of this, the parties of the centre-left, like the Liberals in Canada and Labour in Britain, attempted an experiment in the 1990s and 2000s that they hoped would bring both rising equality and rising prosperity: A largely free and unfettered market economy, combined with low government debt and big investments in social services. The idea was that the booming economy would finance a state-supported rise in equality. The experiment mostly failed: While life did improve for the poor in the West, it didn’t change at all for the middle class, and often got worse, as they watched the wealthy become ultra-wealthy. The increasingly angry “squeezed middle” are the people who tend to vote in elections, and many were driven to distrust the big parties whose experiment failed them.

The big box is closed

The big-tent parties functioned, during their glory years in the postwar decades, as the paternal overlords of protected, closed national economies, engaging in brokerage politics whereby the fruits of growth could be spread out among clients and beneficiaries on the left and right. The big political parties were like family heirlooms, their loyalties kept for life and passed on between generations – badges of personal identity, like Ford and Chevy, Coke and Pepsi, Apple and Microsoft. Membership had its benefits.

But then, in the 2000s, there was what Bruno Cautrès, a political scientist at Paris’s Institute of Political Studies who analyzed dozens of elections, calls a “generational rupture”: Suddenly, he says, voters no longer see parties as badges of loyalty or symbols of lifelong personal identity, but as consumer products, as tools that can be used to address specific concerns.

The new, more open and borderless world of the past 20 years has meant that the big centrist parties continue to work well for the winners, for the in-groups that benefit from their specific programs. But for those who become disconnected or distanced from the state, who have no daily need for government (as the very poor do) but also do not feel its benefits (as the wealthy do not), the big party no longer means anything.

“Since the opening up of the world after the end of the Cold War, we’ve see that mainstream parties find it increasingly difficult to present political programs that address winners and losers at the same time,” says Mr. Cramme. “You basically have both left and right-wing mainstream parties essentially speaking to winners – and all those who are left behind due to globalization, technological change, cultural disaffection, are not adequately represented by mainstream political parties, so we see a surge of extremist parties on both the right and the left.”

This helps explain one of the paradoxes of the moment: The range of political views in most countries has not become more extreme; there are about as many left-wing people and as many right-wing people as before, and fringe views haven’t increased much. But the parties of the fringe have expanded dramatically. Until recently, the big parties of the centre were able to absorb voters with a strong dislike of immigrants or of capitalism, offer them some token recognition, and reward them with the benefits of mainstream power. Now, in a tougher age, that power means little, and the big ideological supermarkets of the democratic world have given way to dusty alleys lined with colourful boutiques.