ISIS -approx 10-20k barely trained lightly armed. Iraqi Army approx 250k

[AnalystInParadise]

21. Actually ISIS has 30,000 fighters

And I think that number is low. Add in the Khorsan fighters, the AQI fighters, the allied Sunni militia fighters and other groups and ISIS can field close to 80-90K fighters. The problem with the Iraqi Army is that it is largely Shia, who will not fight to liberate Sunnia areas. (The areas ISIS controls).

Additionally ISIS now has a few dozen American Abrams tanks and Bradley fighting vehicles and if RUMINT is to be believed a few dozen Americans of prior military service who are maintaining them and training ISIS how to use them in battle.

In many battles ISIS is better equipped and organized than the Iraqi forces, many members of ISIS have experience against U.S. forces and have learned much from us. The Iraqi Army is largely a constabulary force that is great at holding checkpoints, but terrible at moving under fire and conducting Combined Arms operations. ISIS seems to have members within its ranks that know how to do that. (Again, I credit that to the American and Euros in their ranks, a sizeable minority of which have prior military service in those nations military's)

As for the Kurds, you are only as good as your competition, they largely fought the old Iraqi Army which again was great at killing civilians, but shitty at fighting actual soldiers with esprit de corps, proper conventional warfare training, and motivation. The Kurds held off the Iraqis because the Iraqis are god awful soldiers, not because the Kurds are ultimate warriors. ISIS on the other hand is a proto-Army modeled on Western military's in battlefield flexibility, certain tactics, and motivation.


http://www.cnn.com/2014/09/11/world/meast/isis-syria-iraq/