I present an account of mass atrocity prevention based on just war theory precepts. This account entails comparisons among policy options and requires selecting the politically feasible option that has the greatest chance of avoiding atrocities. Adopting such an account of atrocity prevention highlights problems in influential mass atrocity prevention policy reports in that they fail to seriously consider nonviolent civil resistance as a mass atrocity prevention tool. Given that sometimes actors may be unwilling to live under the status quo, and agitate for reform by violent or nonviolent means, nonviolence is generally the preferable policy option. This is because under realistic scenarios, the empirical evidence generally indicates that nonviolent means are more likely to achieve positive outcomes across a range of indicators than violent ones. I illustrate my argument by applying it to strategies for democratisation, and rebut objections. Yet, nonviolent civil resistance is risky, and so revolutionary leaders and their supporters should weigh carefully the chances of success and the trade-offs of nonviolent resistance.