Countries at civil war differ across a number of dimensions that are often used to account for onset, duration or severity. A relatively understudied dimension is the role of institutional arrangements on the severity of civil wars. We argue that federal systems put in place the mechanisms to make civil wars shorter but bloodier because they often allow for independent militia, taxation, and infrastructural development. Federal systems also make more credible a declaration of independence. These factors make civil wars looks much more like conventional warfare than their guerilla-based counterpart. We rely on the cases of Yugoslavia and the United States to build and describe our arguments and then we test our arguments against cross national data from the 20th century civil wars. Our results provide insights into the role of institutional arrangements on the management of internal conflicts and suggest that further research could make an important contribution to our understanding of civil wars.