This dissertation explores and answers two puzzles about states supporting proxies in civil wars. The first puzzle asked why states external to a civil war decided to provide support to a proxy instead of intervening with their own armed forces? In other words, I examined the foreign policy of proxy war where a state’s support for the government in parallel with a state’s support for the opposing side transforms the civil war. While recent scholarship presented various incentives and constraints specific on proxy war, my theory analyses strategies which explain how in a competitive strategic setting a state’s preference led to supporting a proxy in a civil war. Examining proxy war as a foreign policy choice that states prefer over other policies, this dissertation finds that states use a set of proxy war strategies in civil wars. A central finding of this dissertation is that states use the offensive proxy war strategy, which is based on rivalry, less frequently than other proxy war strategies which are based on security, interest, or revenge. However, when both external warring sides use an offensive proxy war strategy these proxy wars may lead to an inadvertent military escalation. Then, I examined a second puzzle pertained to sponsorship relationships and various types of support handed over to proxies. I observed that the type of a sponsorship relationship does not seem to influence the level of support a state will provide. It is the chosen proxy war strategy which influences the type of support states provide to their proxies. Scholars of conflict rely on the delegation model and the orchestration model of indirect governance to describe the relationships that states forge with their proxies. I claim that proxies bargained the authority a sponsor has over them depending on their vulnerability and their identity. I found that recent sponsorship relationships in proxy wars tend to resemble the orchestration model rather than the delegation model. These findings are based on examining all post-Cold War proxy wars through 2016, using Qualitative Case Analysis. I use the fuzzy set variant to test when states chose a proxy war strategy in a civil war. I combined this approach with Set-Method Multimethod Research to explore the inferential mechanism of typical cases of proxy war, in Syria (2011 – 2015), Burundi (1993 – 2003) and Azerbaijan (1991 – 1992). This dissertation’s original contribution is the presentation a proxy war concept which uses the framework of sponsorship relationships based on bargained authority. The dissertation’s theoretical and empirical results uncover generalizable patterns in proxy war strategies in civil wars that directly address scholarly and policy debates in the foreign policy decisions of intervention in civil wars, limited war, indirect governance during conflict, and concept measurement in international relations.