In the past years devastating terrorist attacks struck major European cities of Olso, Paris, Brussels, Nice, Berlin, London, Stockholm, and Manchester. It pushed the response capacity of Europe's emergency management agencies to its limits. Despite of organizational and technological systems being in place, the emergency response fell short on several occasions. After the attack at Zaventem ... [Show full abstract] airport in Brussels, fire and rescue crews operated alongside one of the unexploded suitcase bombs for hours, which later spontaneously detonated. In Manchester, fire crews were ordered to stand down by their commanders who believed the scene was too dangerous, to the dismay of the general public, while police and ambulance crews were working on-site. These cases show that responding to such devasting terrorist attacks typically generates fragmentation: the breakdown of collaborative action and sensemaking. The problem is that we do not really know how to mitigate the negative effects of fragmentation, or pinpoint the circumstances under which fragmentation is functional. This makes fragmentation one of the toughest and least understood challenge in emeregncy response. To overcome this challenge, I will perform a case study of attacks across Europe to explain how crisis managers deal with fragmentation. I will answer the following research question: how do crisis managers adapt their command tactics to manage fragmentation, and to what extent does their adaptation influence the effectiveness of crisis management operations? Answering this question enables a reflection on how to overcome the challenge of fragmentation.