On Monday night, Quebec politics underwent its most significant realignment in the last half-century.

Two parties that had been on the margins — the centre-right Coalition Avenir Québec and left-wing Québec Solidaire — entered the mainstream.

And they did so in dramatic fashion, tossing aside the federalist Liberals and the sovereignist Parti Québécois like old pairs of socks, too stale to keep around.

Not since 1970 has a party other than the Liberals or PQ held power in Quebec.

In the intervening years, Quebec politics lurched away from the state-building projects of the Quiet Revolution to constitutional wrangling and referendums.

The Liberal-PQ antagonism meant the province was left without a conventional left-right spectrum.

Over time, the PQ became a jumble of fiscal conservatives, ardent nationalists and social democrats.

Québec Solidaire's Manon Massé led her party to its best-ever performance, winning 10 seats. (Peter McCabe/The Canadian Press)

The Liberals, meanwhile, could take the support of federalists for granted, as well as anyone spooked by the prospect of yet another referendum.

Sensing the federalist-sovereignist stalemate was frustrating voters, Legault gambled in 2011 by launching a party that would be a nationalist "third way."

It paid off with a decisive victory Monday night that turned the incumbent Liberal Party into a shadow of its former self.

When the dust settled, the Liberals were left with less than 25 per cent of the popular vote, their worst showing since Confederation.

The PQ also reached a historic low in the popular vote. Its seat count was eclipsed by Québec Solidaire, a party whose base was confined, it was thought, to the Montreal hipster haven of Plateau–Mont-Royal.

The CAQ's François Legault invites Quebecers to 'start working together,' while the Liberals' Philippe Couillard reflects on his future, PQ Leader Jean-François Lisée steps down and Québec Solidaire's Manon Massé celebrates her party's rising fortunes. 1:17

New options

Of course, Legault's victory could be simply attributed to fatigue with the Quebec Liberals.

They have been in power for 13 of the last 15 years, often amid allegations of corruption and patronage.

But that ignores deeper social changes that have been underway in Quebec for close to a decade, and Monday night's results represent something of a culmination of that movement.

The advent of the CAQ government and the sudden rise of QS can be seen as two sides of the same phenomenon: the replacement of the sovereignist-federalist cleavage with a more conventional left-right spectrum.

Frédéric Boily, author of a recent book on the CAQ, details four recent developments in Quebec that help explain why this realignment happened now.

The first is a generalized sense of ambivalence about Quebec's electoral institutions.

"There is a current crisis of confidence about democracy that is more significant in Quebec than it is elsewhere in Canada," Boily said in an interview before the election.

When the dust settled, Philippe Couillard's Liberals were left with less than 25 per cent of the popular vote, their worst showing since Confederation. (Mathieu Belanger/Reuters)

For Boily, that helps explain why Quebecers may be more willing to experiment with unconventional options in the ballot box.

Quebec also underwent a series of political experiences that pushed them to think beyond the sovereignist-federalist divide.

There is the ongoing anxiety over how to accommodate religious and cultural minorities in the province. Identity politics has taken up more space recently than talk of sovereignty.

Quebecers also developed strong negative opinions about former Conservative prime minister Stephen Harper, said Boily.

Perhaps because of that, "Harper was careful not to provoke any constitutional quarrels with Quebec, and it contributed to reinforcing the left-right agenda," he said.

Finally, there were the student strikes of 2012 which eventually morphed into large-scale protests against the Liberal government at the time.

Opinion about the strikes was polarized in the province, with many thinking the student demands for a break on tuition fees were unrealistic.

The months-long student protests further entrenched left-right thinking in the province. They also helped launch the political career of one of the student union leaders, Gabriel Nadeau-Dubois, now co-spokesperson of QS.

Parti Québécois Leader Jean-François Lisée with daughter, left, and partner Sylvie Bergeron as they watched election results come in on television in Montreal. (Graham Hughes/Canadian Press)

Room enough for everyone?

The last time Quebec witnessed a political realignment of this magnitude was 1970.

Then as now, there were four main parties jostling with each other for a share of the vote.

Quebec's political system ultimately consigned two to the dustbin of history, the conservative Union Nationale and Ralliement créditiste du Québec, a social credit party.

It took a few election cycles for this to play out. But Quebec politics finds itself at a similar crossroads on Tuesday morning.

Thanks to a couple of newcomers, the political scene is now crowded again, and there might not be room enough for everyone.