Existing studies argue that external support to rebels increases their extent of violence against civilians while also intensifying fighting. While these studies assume a homogenous effect of external support on conflict dynamics, we argue that the effect of external support depends on the structure of the support relationship between a state sponsors and a rebel group. We suggest differentiating between two modes of external support – delegation and orchestration – that vary with regards to the hierarchical control they provide sponsors as well as their incentive to exert control over rebels. We hypothesize that delegation increases combat deaths, while orchestration increases rebels’ violence against civilians. Results from an analysis using global data on rebel sponsorship and armed intrastate conflict for the period 1989-2009 support our theoretical expectations. Our findings point to the need of enhanced international monitoring of clandestine support – orchestration – to decrease sponsors’ incentives to sacrifice control and thus limit atrocities in civil wars.