Civil war theory testing: How greed, horizontal inequalities, and institutions explain the Yemeni civil war between 2004 and 2009? This article applies a comparative design to test the explanatory power of formal quantitative models of civil war. It examines the grievance, horizontal inequalities, and institutional models of civil war through the case study of the Yemeni civil war between 2004 and 2009. The aim is to highlight political processes that culminate in civil war, and to account for omitted variables in theories of civil war. In the Yemeni case these variables were the competitive rebel market and tribalism. The article shows that civil wars are not isolated events, but parts of a cycle of violence. By accounting for micro-level motives the causal processes that lead to civil wars can be better understood.