Throughout history, waves of collective action often occur in and around wartime. However, the relationship between war and collective action is not often systematically examined is therefore the focus of this project. The focus is on Belgium and the two world wars. The following questions are central. How can we explain that the wars had such an impact on the patterns of collective action? To what shifts in political opportunity structures can these shifts be attributed? What was the impact of the wars on the intensity of protest and the action repertoires used? Did the war lead to the collective mobilization of new types of actors (e.g., former deported workers or war widows)? Did the wars have a lasting effect on patterns of collective action.