•We analyze the role of large floods on the onset and prevalence of internal armed conflict.•We focus on the displacement induced by floods as a determinant of armed conflict.•We address the endogeneity between the displacement caused by large floods and armed conflict.•Flood-induced displacement does not ignite new conflict, but it fuels existing conflicts.•This effect is larger in developing countries and it recedes with time. Large, catastrophic floods intensify environmental scarcity and can lead to mass displacement from affected areas. The sudden and mass influx of migrants could increase the risk of social tensions in receiving areas. In this paper, we analyze the impact of the displacement induced by large floods on civil conflict using historical data for 126 countries during 1985–2009. Our results suggest that while the displacement caused by large floods did not ignite new conflicts, it fueled existing conflicts. This effect was larger in developing countries and it receded with time, vanishing five years following the flood.