 Both studies focusing on specific historical societies and analyses of cross-cultural data have failed to find positive correlation between population density and incidence of warfare.Korotayev, in collaboration with Peter Turchin, has shown that such negative results do not falsify the population-warfare hypothesis.Population and warfare are dynamical variables, and if their interaction causes sustained oscillations, then we do not in general expect to find strong correlation between the two variables measured at the same time (that is, unlagged).