You need to read the article

The Atlantic has the most intelligent comments about terrorism that I have ever read. The basic point, as I interpret the article, is that we don't know enough about the subject. This lack of knowledge is in direct contrast to our experience in World War II and the Cold War. I can't effectively summarize the article, but here are some of the comments the authors, who have spent most of their work life trying to understand terrorism, made.

I am continually surprised by how many submissions treat terrorism as something that began on 9/11 and whose authors seem to be unaware of the wealth of research and literature which predated that watershed event. Similarly, the fashion in terrorism studies today is highly methodological treatments replete with voluminous accompanying tables, figures, graphs, and statistical interpretations. While impressive in a purely technical sense, I often find little in them that is either new or genuinely advances the field or improves our understanding of the phenomenon.
There is also an understandable “herding” aspect to contemporary terrorism research around whatever the issue or threat du jour happens to be. It was suicide terrorism a decade ago, radicalization more recently, and “lone wolves” today. Less common in my experience are submissions that focus less on what is topical and in the news and more on what is unique, unusual, trendsetting, anticipatory, or novel. The literature on terrorism that authoritatively draws on historical comparisons, contemporary analogues, new theoretical interpretations, or truly innovative approaches seems to have become far less prevalent in recent years.I would add that much as we still lack an understanding of why persons become terrorists, we also still lack an understanding of how governments can best and most effectively respond to this menace.
In this respect, the fact that terrorism is a strategy of provocation is often forgotten or neglected. Terrorists have arguably always attempted to provoke governments to react emotionally and precipitously to threats rather than respond in a sober and rational manner. Many critics charge that this is precisely what happened in the aftermath of the 9/11 attacks with the declaration of an expansive “war on terror.” Yet, governments seem to have continually fallen into this trap—with the predictable result that we remain enmeshed in spiraling cycles of violence and campaigns with no end apparently in sight.
Hand-in-glove with this is a failure to understand that terrorism is also a strategy of attrition. It is designed not only to wear down the terrorists’ government opponents and undermine the morale of both the authorities themselves and the citizens they either represent or are charged with protecting, but also over time to create deep fissures in national polities, to undermine public confidence in elected leaders, to foment paranoia and xenophobia, and thus cause liberal societies to adopt increasingly illiberal means to enhance security and supposedly better protect and defend against this threat. One just has to look at the divisive debates and political campaigns today in the United States, Germany, and elsewhere to see the corrosive effects that this terrorist strategy is having on our societies and political systems.
The tendency to oversimplify what is an extraordinarily complex phenomenon is still very much with us, especially with policymakers. People want to see terrorism through one prism. Or to see it in binary terms: It is either the work of evil fanatics or of misguided youth. The messy reality is hard to deal with. For many years researchers have been trying to explain that there is no single “terrorist profile,” but such a profile still seems to be the holy grail. There is a notion that on 9/11, the world changed, and in many respects it did. But that has become a basis for discarding what happened and what was learned before.
It would be incorrect to say that civil liberties have been savaged, but we have laid the foundation for what, under a less benign government or a more frightened populace, could become a more oppressive state.

We have survived more than four decades of terrorism. People are shocked when I point out that during the 1970s, the United States survived 50 to 60 terrorist bombings a year. Imagine that volume of terrorist activity today. We need to take terrorism seriously, but we ought not to inflate the terrorist threat.
Terrorism involves not just the terrorists and their counterterrorist adversaries. Terrorism is aimed at the people watching. It is intended to produce fear, which will, in turn, cause us to exaggerate the threat. And it often works. Research focuses on the terrorist threat and the countermeasures. We devote less attention to the reactions of the audience. We don't want to look at us.
Accordingly, one has to wonder whether from the terrorists’ perspective they think they are losing. The threat posed by ISIS’s caliphate may soon prove to have been a flash in the pan, but the fact that al-Qaeda has survived the greatest worldwide onslaught ever directed against a terrorist group by the most technologically advanced military in the history of mankind underscores how much more challenging counterterrorism is today compared with the 20th century—when many left-wing groups were small enough to be crushed by police action or simply outlived their relevance.
The terrorists have a second advantage. It is inherently less difficult to exploit anger and fuel violence than it is to bring or restore order. In continuing efforts to combat terrorism, the United States must be cautious not to assume the mission of removing every tyrant, fixing every failed state, eliminating every ungoverned space—in other words, reconstructing and policing the world. As we reflect upon 9/11, one poll asked whether the world is now a safer place. Is that America's burden?
Martha nails it when she writes that our enemies' conception of success and victory are vastly different than our own, and that losing the caliphate is, in their eyes, a mere tactical reversal. When a struggle is divinely ordained—as both al-Qaeda and ISIS claim theirs to be—all temporal setbacks or defeats are inconsequential and mere speed bumps on the highway to triumph: challenges deliberately put in the terrorists’ path to test their fealty and ultimate commitment to the cause and the group that they serve.