For the most part, ISIS has lost pretty much every battle/conflict they have instigated. They fought Iraq and got slaughtered, the same thing happened in Russia. On top of that since august America AND Russia have been bombing the shit out of ISIS compounds and territory witch has proven to be very effective, they even airstriked the oil rigs owned by ISIS (witch is their main source of funding). All of this combined has caused them to lose tons of resources like ammo, heavy vehicles money and manpower to continue fighting.