The forces of the Islamic State may no longer control a swath of territory across Iraq and Syria, but the coordinated attacks in Sri Lanka demonstrated that the resilient group can still sow carnage beyond the borders of its former “caliphate.”

Even a landless Islamic State is influential, as a facilitator of attacks and an inspiration for its followers, including the ones who blew themselves up in churches and hotels Easter morning, killing at least 359 people, terrorism experts said.