One bit of good news about the two shocking attacks on our nation this week is that they were not the work of organized groups. They appear to have been carried out by individuals – both self-radicalized and deeply troubled – who latched on to a toxic ideology and acted alone.

"Lone wolf" attacks don't kill very many people, but they can be extremely destructive to society if we allow them to be. They can also be very hard to intercept. People who get together to plan organized mayhem (the "Toronto 18," the alleged Via train plotters) are easier to detect and disrupt than people acting on their own.

The two killers were both on the radar screen, and to that extent, the system worked. But setting aside the security issues on Parliament Hill, it isn't clear that either man could have been foiled in advance. Murderous thoughts alone aren't enough to get someone locked up. Endless raving about the criminal Harper government's complicity in imperial wars against the Middle East is perfectly legal. (If it weren't, our jails would be stuffed with activists and university professors.)

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Some people are going to argue that the killers – especially Michael Zehaf-Bibeau, the Parliament Hill shooter – were really mental-health threats, rather than terrorism threats, and that by labelling them terrorists we are misdiagnosing the real problem. But no matter how sane they were, both were deadly. Mr. Zehaf-Bibeau didn't put on a kaffiyeh and assume the glorious martyr's pose for nothing. There are reasons why the jihadi cause is such a magnet for the troubled, the lost and the unhinged – what are they?

One reason is that these men are not, in fact, alone. The world is full of Islamic State fanboys, more than we would like to think. They nurture their rage and fantasies on the Internet, and they form a relatively large community of people who think that beheading Westerners is cool. Anyone can become a member. Society's misfits and outsiders can become insiders online. They can even aspire to greatness through martyrdom.

Liberal Leader Justin Trudeau was right when he said these attacks were criminal acts, not religious ones. The trouble is that both the killers and the fanboys believed otherwise.

Jihadi radicalization is here to stay, maintains Peter Neumann, who directs the International Centre for the Study of Radicalisation in London. We can't prevent it; we can only do our best to manage it. The most important question is the changing nature of the conflict, not whether we're witnessing a surge of dangerous attacks – we aren't, although it certainly feels that way this week.

The biggest qualitative difference between 9/11 and today, Mr. Neumann says, is the Internet. Another change is the move away from calculated acts of strategic terrorism (Madrid, London) and the rise of large numbers of unorganized jihadi amateurs. The third change is the emergence of aspiring foreign fighters, and their ability to cause disruption here at home. He promises that these challenges will keep us busy for years to come.

Of course, there's another school of thought about root causes, arguing that we've brought this on ourselves. This group, too, is larger than you might think. It includes journalist Glenn Greenwald, who vilified the government's response to Monday's hit-and-run murder of a soldier in an online screed.

"The right-wing Canadian government wasted no time in seizing on the incident to promote its fear-mongering agenda over terrorism," he wrote Tuesday, before the attack on Parliament.

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"… It is always stunning when a country that has brought violence and military force to numerous countries acts shocked and bewildered when someone brings a tiny fraction of that violence back to that country. Regardless of one's views on the justifiability of Canada's lengthy military actions, it's not the slightest bit surprising or difficult to understand why people who identify with those on the other end of Canadian bombs and bullets would decide to attack the military responsible for that violence.

"That's the nature of war. A country doesn't get to run around for years wallowing in war glory, invading, rendering and bombing others, without the risk of having violence brought back to it."

It's not about "justification," he argued, but "causation."

Mr. Greenwald, who happened to be in Canada this week for several appearances, may have a point – but as international politics expert Dan Drezner points out, it isn't much of one. By this reasoning, half the nations of the world should be awash in terrorism right now. As bellicosity goes, our small and rather unimportant country is way down the list.

But "blowback" is an explanation beloved of many. You could call it an expression of the Fiskian worldview (after journalist Robert Fisk), which blames all our troubles on our wicked meddling in places where we don't belong. "Chickens coming home to roost," tweeted Alex Hundert, the leftist hero of Toronto's G20 protests, after Wednesday's attack. On rabble.ca, frequent essayist Murray Dobbin opined, "We prefer denial and the simplistic – the notion that we can correct 25 years of imperial hubris, ignorance and gross incompetence by Western powers by bombing our own creation." (That was published on Monday.)

You can be for or against our participation in the bombing of the Islamic State. I could argue it either way, myself. But it's ridiculous to argue that chaos in the Middle East (not to mention Afghanistan, Pakistan and large parts of Africa) is all about us. Mainly, it's about a Shia-Sunni conflict that goes back centuries, and a particularly malevolent perversion of Islam.

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I suspect Mr. Greenwald will be sorely disappointed if Canada doesn't devolve into a police state. But for that to happen in a democracy, the people must be very, very frightened. And we're not. We're rattled – but we're fine.