But the other big news was the extraordinary breakthrough of the New Democratic Party, a left-of-center grouping with roots in prairie populism and the trade union movement that was long Canada’s third party. Their rise was a tribute to the personal appeal of the party’s leader, Jack Layton, and allowed the NDP to eclipse the Liberal Party as the official opposition.

 The centrist Liberals had for more than a century been something close to Canada’s natural governing party. It was said that the Liberals often campaigned from the center-left, but typically governed from the center or even center-right. To understand how revolutionary this transformation is, imagine the U.S. Democratic Party being replaced as the main alternative to the Republicans by a Progressive Party to the Democrats’ left.

 It takes nothing away from Harper’s victory to note that he would probably not have secured his majority if the New Democrats and the Liberals had not so closely split the opposition vote in key parliamentary districts — or “ridings,” as the Canadians call them, particularly in Ontario, the country’s largest province. I wrote about the possibility of such a split on the center-left, and it came to pass with a vengeance.

 Nationwide, the Conservatives received 39.6 percent of the popular vote, to 30.6 percent for the New Democrats and 18.9 percent for the Liberals. The separatist Bloc Quebecois secured 6 percent of the national vote, all from Quebec, and the Green Party got 3.9 percent. In other words, taken together, the NDP and the Liberals secured roughly 10 percent more of the popular vote than the Conservatives did — and if you add in the Greens, you could make the case that the broad center-left secured 53.4 percent of the total vote. A Conservative might justly argue that an amalgamated center-left party would get fewer votes in a head-to-head battle with the Conservatives than each of its component parts now get separately. Nonetheless, a substantial majority of Canadian voters chose a party other than the Conservatives.

Yet the Conservatives translated their 39.6 percent into a healthy majority of seats, winning 167 to the NDP’s 102, 34 for the Liberals, 4 for the Bloc Quebecois and one Green. (Elizabeth May, the Green leader, became the first of her party to win a seat in Parliament.) Eric Grenier of ThreeHundredEight.com argues in the Globe and Mail this morning that absent vote-splitting between the New Democrats and the Liberals, the Conservatives would have won 151 seats, four short of a majority.

 The Conservatives’ gains were large and the NDP’s were staggering. In the outgoing Parliament, the Conservatives had 143 seats, the NDP 36, the Liberals 77, and the Bloc Quebecois 47. The NDP’s greatest gains came in Quebec, where they mostly took seats from the Bloc, nearly wiping out the party.

There is much to say about these elections, and I commend the Globe and Mail’s Web site, which is chock full of interesting analysis. I’ll confine myself to three quick observations.

First, this is obviously a big opportunity for Harper and the Conservatives, but the question is: Which opportunity does Harper see? Does he use his majority to push through a strongly conservative agenda? Or does he pursue a more moderate brand of conservatism? With the Liberal Party potentially facing dissolution, there are conservative-leaning voters in the Liberals’ broad middle-ground coalition who could go with a moderate Conservative Party — but not a hard-line party. Michael Ignatieff, who led the Liberals in this election and resigned as leader on Tuesday after losing his own seat, expressed the hope of middle-ground Liberals that “four years of Conservative right-wing government” would lead to a Liberal revival. Perhaps. But Harper has proven himself to be an adept politician and may not fall into the trap Ignatieff described.

 In any event, will the Liberal Party be there? The other great opportunity is Layton’s. He can build the NDP into a broad opposition party and turn it into the main alternative to the Conservatives. But first he will have to deal with a complicated caucus swelled with members from Quebec, many of them inexperienced in politics. Indeed, many of them never expected the NDP sweep and thus never expected to get elected in the first place. In the meantime, the Liberals will be holding a great internal debate: Do they maintain their identity as the party of “the vital center,” as Ignatieff proudly called them, rebuild on their own and hope that the Conservatives and the NDP stumble? Or do the Liberals align with the NDP and create a broad center-left party or coalition? 

Whatever the Liberals decide, there is a lesson for American politics from Canada: Confronting a cohesive conservatism, progressives win only when the center and left come together.

Finally, there is Quebec. The election was a great defeat for Quebec separatists who have fought for decades to make their province an independent, French-speaking nation. Yet don’t count the nationalists out yet. By opting overwhelmingly for the NDP and against Harper’s Conservatives, Quebec underscored its distinctiveness. This could feed the sort of alienation on which separatist sentiment grows.

 Layton’s NDP has its Quebec votes on loan. Dealing with his vast new following in Quebec will be another great challenge for Layton. Still, nothing can take away from the fact that for the first time in the history of Canada or the United States, a party with social democratic roots has emerged as the main challenger to political conservatism.