In this article, we offer an explanation for varying patterns of territorial reforms aimed at accommodating claims for more substate autonomy inmultinational states. We argue that the interaction between preferences of state-wide and non-statewide parties, their negotiation power and the negotiation mode accounts for specific patterns of territorial change. Analytically, we advance existing research in two ways: First, by analyzing territorial change in a two-dimensional space (vertical and horizontal), we pay explicit attention to jurisdictional heterogeneity between substates. Second, by applying an actor-centered institutionalist approach, we highlight the strategic potential of actors within the institutional setting. The comparative analysis of thirteen processes of territorial change in four multinational Western democracies-Canada, Belgium, Spain, and the UK-reveals, first, certain conditional effects of the independent variables on specific patterns of territorial change and, second, how the negotiation mode impacts on a party's negotiation power.
