ISIS just claimed a major new terror attack in the Belgian capital of Brussels. To understand why they would do this, you have to look at something that changed for ISIS about a year ago and pretty far away in the middle east.

So ISIS in the summer of 2014 had had a massive sweep across the region, seizing lots of cities. Starting in early 2015, the group began to suffer some real defeats in Syria and Irak, lost some major cities, and began to come under attack from American airstrikes and in just a few months it lost a quarter of its territory. But this posed more than just a military threat to ISIS. It had always operated on the narrative of victory and invincibility, and it used that to recruit and motivate fighters from other Jihadist groups. It needs those fighters for the caliphate survival. But when it started losing ground so it was also losing that narrative and it needed something new to keep that going. So first they tried to expand abroad, in Libya, Afghanistan, Yemen, but those efforts all fizzled, in the summer and fall of 2015.

ISIS found its solution, by launching mass terror attacks against civilians abroad and this helped the group portray itself once again as on March 2016, but then Europe faced a significant problem in how to deal with these attacks because the hard truth is that most of these attackers aren’t foreigners. They aren’t refugees or migrants; they’re actually European nationals, and you can’t just close the border to keep them out if they’re actually from Europe. Lots of them are people who went and joined ISIS or other terrorist groups, so-called foreign fighters.

Now, that ISIS is losing territory, those fighters are coming home, and they’re bringing their battlefield hardened experience and skills with them. These are really hard problems to solve, rooted in socio-economic problems grievances that go pretty deep in the European society; you can’t solve this with bombs or with border closings.

So what now?

It seems likely that as ISIS keeps losing its territory, it is going to become something like what it was before when America was fighting in the Iraq war in the mid-2000’s: not a state, but still an insurgency and a terrorist group capable of doing terrible damage abroad.