Recent events have raised questions about the extent to which military intervention promotes democracy and the degree to which this depends on the nature of the intervener. We argue that traction on these issues is best obtained by focusing on the policies of the target state that have the greatest implications for the political survival of the intervening state s leader and the kind of governmental institutions in the target state that are most likely to produce them. This perspective generally although not always predicts that third-party military intervention in civil wars, other intra- or interstate disputes and wars will lead to little if any improvement, and all too often erosion in the trajectory of democratic development. Three hypotheses on the impact of third-party intervention by democracies, autocracies, and the United Nations are then tested and strongly supported against a counterfactual expectation of what the democratic trajectory would have been in the absence of intervention.