Contemporary research attempts to uncover what drives civilian casualties and conflict duration in civil wars. This thesis employs the controlled direct effect (CDE) method to detect whether sanctions placed on states providing support to foreign rebel groups have potential to reduce civilian deaths and reduce conflict duration using a cross-national quantitative analysis. The findings suggest that while sanctions might be effective in reducing the duration of the conflict, the resulting cessation of support does not generate higher civilian casualties. The findings are then subject to a qualitative evaluation based on Russian support for separatist rebels in Georgia and Ukraine, also upholding only some arguments of the paper.