What role does nonviolent action play in ending civil wars? Previous research has discounted the degree to which grassroots, nonviolent mobilization might generate conditions favorable to civil war termination. In this paper, I draw on cases like El Salvador, Liberia, South Africa, and Libya to lay out different possible mechanisms by which nonviolent, civil resistance might initiate the end of an ongoing civil war. I then identify different issues that arise with regard to researching this particular question, and lay out several possible ways forward in evaluating the potential of these mechanisms to play out in other civil war cases. I conclude with suggestions for further research and policy implications.