Actually , Many rebel groups are directly fighting against ISIS . The MO of ISIS has been to wait until Rebels liberate an area from the regime , then swoop in and take it from the Rebels . Rinse , lather , repeat . ISIS has rarely engaged the regime in battles around 3 or 4 since 2012 . ISIS has a long battle front with the regime that really is not active at all . Also , the regime has a history of using Jihadis to manipulate political situations , see the Iraqi government complaints in 20062007 about the Syrian regime sending Jihadis across the border . Additional disclaimer Of course , there are rebel groups that are sympathetic to ISIS . Source I am Syrian , and have been following the situation in Syria since the outbreak of protests in 2011 .