Decentralisation, the transfer of power from the central state to the regions, is often seen as a way to pacify conflicts between ethnic groups in divided states. However, sceptics argue that decentralisation would rather add to the conflict. Research on this ongoing debate usually focusses on (amongst others) violent ethnic conflicts, or on the impact of decentralisation on separatism or regional identification. This is only part of the story. Whether decentralisation can lessen the polarisation between ethnic groups (by allowing them to go their own way when common policy-making becomes infeasible), and whether it can ensure that there are less conflicts between ethnic groups and that these groups are better able to solve conflicts, has received surprisingly little academic attention. Yet, these are also important reasons why many states, and particularly Western states, have opted for decentralisation reforms. Our study wants to address this lacuna. We do so by studying a critical case -Belgium- over a long period of time. Using time series analyses, we evaluate the impact of decentralisation on (1) the policy disagreement between Flemish and Francophone elites (1978-2019) and (2) the extent to which they manage to negotiate and solve conflicts together (1945-2019). In this effort, we will not only study the impact of decentralisation in its entirety, but we will also test whether this impact has been even more manifest after 1995 (a milestone on several levels).