This article reexamines the democratic peace in a longitudinal fashion. We extend the democratic peace proposition beyond isolated militarized disputes or wars to longer term interstate rivalries. Rivalries of all types are rare among democratic dyads; there is only one case of enduring rivalry between consistently democratic states, and most conflictual relationships between democracies remain confined to isolated conflict. Second, we assess the effect of regime change on rivalry behavior when a regime change precipitates or ends a jointly democratic dyad. Enduring rivalries that include both joint democratic and nondemocratic periods exhibit significantly lower dispute propensities while both rivals are democratic, although proto-rivalries show much smaller differences. Importantly, the pacifying effect of democracy appears to strengthen over time after the transition to joint democracy, which is consistent with the onset and deepening of democratic norms. Both proto- and enduring rivalries show a decreasing propensity for militarized conflict within a year of the transition to joint democracy, and this propensity decreases almost to zero within five years. Our results generally confirm and extend the robust effects of the democratic peace.