Story highlights Dozens were killed in Brussels on Tuesday in attacks on airport, subway station

Juliette Kayyem: Too many soft targets in Europe and the United States to ensure complete security

CNN national security analyst Juliette Kayyem is a professor at Harvard's Kennedy School, a former assistant secretary of Homeland Security in the Obama administration and founder of Kayyem Solutions, a security consulting firm. She is the host of the "Security Mom" podcast and author of a forthcoming book, "Security Mom: An Unclassified Guide to Protecting Our Homeland and Your Home." The opinions expressed in this commentary are hers.

(CNN) The attacks Tuesday morning on the airport and a subway station in Brussels were highly probable, and at the same time almost impossible to disrupt. That oxymoron is what makes this wave of terrorism the most dangerous in history, and so different from even the days of al Qaeda.

As I wrote last week , the arrest on Friday of Paris terrorism suspect Salah Abdeslam was never going to be the end of the fight. Indeed, it could possibly be the beginning of a new wave from ISIS.

Because Abdeslam was captured alive, European authorities were likely going to be able to get him to speak and perhaps reveal details about the network that had aided him in the Paris attacks last year and that let him remain in hiding for months after. And even absent any willingness to speak on his part, Belgian officials would have been more than willing to make it appear as if he were cooperating. Indeed, as early as last weekend, Belgian officials were saying that Abdeslam was "collaborating," a word that makes it sound like he was more than happy to turn over information.

Juliette Kayyem

Those in his network, or those who support ISIS, were likely to feel the pressure and launch attacks if they had the opportunity. So why, many are asking, wasn't Brussels ready for another attack?

Basically, no country is ever completely ready.

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