Foreign fighters have fought on all four sides of the Syrian Civil War, as well both sides of the War in Iraq. In addition to Sunni foreign fighters, Shia fighters from several countries have joined pro-government militias in Syria, leftist militants have joined Kurdish fighting forces, and other foreign fighters have joined jihadist organizations and private military contractors recruit globally. Estimates of the total number of foreign Sunnis who have fought for the Syrian rebels over the course of the conflict range from 5,000 to over 10,000, while foreign Shia fighters numbered around 10,000 or less in 2013 rising to between 15,000 and 25,000 in 2017.