Motivated by the war in Syria and the ascension of ISIS, this paper models a proxy war with three sponsors and three combatants as a dynamic game. Sponsors are leaders that provide resources for combatants to fight each other. Sponsors 1 and 2 have strong aversion to sponsor 3's proxy, but not against each other. Three pure strategy equilibria exist in the game. When the ex post value of winning is small, all players fight in equilibrium. However, when the ex post value of winning is large, in equilibrium either sponsors 1 and 2 coordinate their actions, with one of them staying out of the contest, or sponsor 3 does not participate. The probability of winning and the sponsors' payoffs depend on a spillover effect. We find that no unique way of characterizing the comparative statics of the spillover effect emerges and that the answer varies from one equilibrium to another.Finally, we identify conditions under which sponsors 1 and 2 would want to form an alliance.Alawite and Druze, who comprise 16% of the population), plus Christians (10% of the population); different ethnic groups -both Arab (90%) and non-Arab (10%); 6 and three broad political groups -the pro-establishment dictatorship of the Baath party, democrats, and Islamic fundamentalists.Each of those combatant groups has one or more sponsors: the United States and western allies, supporting political opposition to the Syrian Assad regime (who they assume think like western liberals); Russia and Iran, supporting the Assad regime (which is thought to represent Syrian Shia, Allawite, Druze, and Christians); and, finally, a loose army of international Muslim Sunni volunteers (an important part composed of Muslim Europeans), supporting and fighting for ISIS.Syria clearly is plagued by communal cleavages. Throughout its history Syria never was an independent country with a uniform ethnic-religious-political composition. After its independence from France in 1946 it struggled to find an identity. The Baath party gave Syria a much needed identity, with an ideology that is a mixture of Arab nationalism and socialism. It has a Bolshevik type of organization that permeates all regions, cities, villages, institutions and groups of Syrian society. The Baath party and the army are the only institutions that allowed a significant share of Syrian society the opportunity for social mobility, in particular for religious minorities, such as the Allawites, which ended up forming the Army's elite.General Hafiz al-Assad's 30-year dictatorship was able to consolidate power because Assad had political influence inside the Baath party and control of the Army (Hinnebusch 2014).The only major segment of Syrian society that was not under governmental influence was the poor Sunni majority, profoundly influenced by the Islamic fundamentalism of the Muslim Brotherhood