Looking around social media, there seem to be two theories about the motive for the attack. Most are guessing that it's a retaliation for the arrest of a terrorist leader in Belgium a few days ago. But other people are saying that an attack like this would take months to plan, so that's unlikely.
Some people are noting that Brussels is a hub for terrorist operations, and it doesn't make much logistical sense to attack your own hub. Those people are saying that this is more likely to be a desperate last-ditch attack by a Belgium-based terrorist cell who are close to being defeated. I think that makes more sense, and I hope it's true.
I'm not looking forward to what this does for the discourse in the United States. Trump will certainly be talking about this. I'm just thankful that most Americans are asleep right now so they aren't watching the events in Brussels unfold live.
Thoughts and prayers for all the dead and injured in Brussels. How horrid.