A man puts up paper to hide the crime scene where two gunmen opened fire in a Quebec mosque during evening prayers on Sunday, killing six people. (Andre Pichette/EPA)

The notion of mass violence in Canada always seems to surprise.

Even two years ago — long after terror and vigilance anecame global conditions — an American politician’s comments about building a border wall through sleepy Canadian forests was ridiculed so much that it helped end his campaign. And gun-wary Canada has long avoided the kind of mass shootings that are epidemic in its southern neighbor.

Then, on Sunday night, there was shock across the world as blood spilled in the north. An apparent terrorist attack on a Quebec City mosque killed six and wounded many more. The premier of Quebec province expressed “horror and incredulity.”

It’s believed to be the first mass shooting at a mosque in North America. But it is far from the first time terrorists have struck Canada — and far from its deadliest such attack.

Police have not yet revealed who has been arrested in the Quebec attack, nor have they speculated about why they might have done it.

Motives were clearer in the summer of 1970.

That’s when a Quebec cabinet minister was abducted off his lawn, strangled and left dead in a car trunk. His killers were homegrown Canadian terrorists — members of a Quebec separatist movement that had bombed the Montreal Stock Exchange a year earlier, as recounted in the Globe and Mail newspaper.

A decade later, international terrorists savaged Canada.

“A bomb exploded in a locker in this city’s main railroad station today, killing three people and wounding as many as 41,” the New York Times reported from Montreal in September 1984. A New York man was arrested, and officials said he was protesting a planned visit by Pope John Paul II. The man was convicted and died in prison in 1993 with an appeal pending.

A year later, an Air India flight took off from Vancouver carrying 329 people and a bomb in a suitcase. The plane exploded over the ocean, killing everyone on board.

The Canadian Press called it “the worst terrorist act in Canadian history.” It had been revenge, the Guardian reported, for a raid on a Sikh temple on the other side of the globe.

Despite all these horrors and many others in the 20th century, Canada maintained a somewhat idyllic reputation — occasionally demonstrated with lax security.

It was not a terrorist but rather a schizophrenic man who one night in 1995 climbed the fence outside Prime Minister Jean Chrétien’s residence, broke a window and paced the hall with a jackknife until the Canadian leader’s wife got out of bed to investigate.

No guards were kept in the Canadian equivalent of the White House, the New York Times reported. Chrétien’s wife had to call the police, lock the bedroom door and wait with her husband for help. “I could not believe what she was telling me,” the prime minister told reporters.

There was another surprise at the turn of the century when an al-Qaeda member was arrested with a trunk full of explosives after crossing the Canadian border on New Year’s Eve 1999. He was later convicted of planning to drive to Los Angeles International Airport and blow it up.

Still, The Washington Post’s Jerry Markon wrote, only 300 American border agents patrolled the 5,500-mile frontier in 2001.

When al-Qaeda flew planes into the twin towers and the Pentagon that year, shutting down U.S. airspace, a tiny town in Newfoundland famously opened its runways — a show of good faith in a new age of terror.

“The people of Gander, a town of no more than 10,000, looked at all those planes lined up at the airport and didn’t think of terrorism, didn’t see potential attacks,” The Post’s Petula Dvorak wrote. “They just wanted to help.”

The Sept. 11 attacks and subsequent wars inspired Islamist plots across the world, and Canada was no exception. In summer 2006, 17 people — mostly teenagers from a Toronto high school — were accused of an elaborate plot to take hostages on Parliament Hill and bomb the city.

“The arrests last weekend left many Canadians pondering how a country proud of its diverse culture and political moderation could spawn such an apparent interest in violence,” The Post wrote.

Plots surpassed mere interest during a bloody week in 2014, when two soldiers were killed on Canadian soil within a few days of each other. In the first attack, a man ran down his victim in a Quebec parking lot. In the second, a man shot an honor guard at the National War Memorial point-blank, then entered the Parliament building and continued firing. “The assault in Ottawa shocked a country that rarely experiences gun violence,” The Post wrote.

Two years later, a Canadian was killed by police in Bangladesh. He was suspected of helping organize the siege of a bakery in which nearly 30 people were slain.

So it goes with Canada and terror. People die, people are shocked … and then the incident fades from the news. The Canadian government does not track terrorist incidents, although a research group has catalogued more than 1,400 attacks and nearly 500 deaths in the country since 1960.

Only a small fraction of those involved guns, many kinds of which are banned in Canada, with extensive background checks required to use the rest. Researchers counted only three mass shootings in the country between 2000 and 2014, according to PolitiFact, compared with 133 in the United States — which has 10 times more people.

But nonpolitical gun violence has begun to trouble Canada, The Post’s William Marsden reported last year. “Worried about smuggled firearms from the United States,” he wrote, “[Canada’s] government is preparing to stiffen its already tough gun laws and step up border surveillance.”

The cross-border wariness is mutual, to some extent. The U.S. House of Representatives passed a bill in 2015 to study threats along the Canadian border, where exponentially more border agents patrol as did at the turn of the century.

Still, that’s the same year that Wisconsin Gov. Scott Walker (R) abandoned his presidential campaign, not long after being mocked for entertaining the idea of walling off the Canadian frontier.

And by last weekend, the image of Canada as a haven from violence was strong once again — at least in the words of Prime Minister Justin Trudeau, responding to President Trump’s bans on millions of foreigners entering the United States.

A day later, a Canadian mosque saw a massacre, and Trudeau grieved with the rest of the world.

An earlier version of this story incorrectly said most kinds of guns are banned in Canada. The story has been corrected.

More reading:

On 9/11, a tiny Canadian town opened its runways and heart to 7,000 stranded travelers

45 years of terrorist attacks in Europe, visualized