STRINGER Iraq/REUTERS
In the early days of ISIS's recent onslaught, the Peshmerga took the oil-rich city of Kirkuk, under the pretense of protecting it after the Iraqi Army fled. Since that expansion of Kurdish control, the Peshmerga has dug in around Kurdistan's borders in an attempt to deter any ISIS advance into its territory.
ISIS would have a serious conflict on its hands if it focused its offensive on Kurdistan. The Peshmerga number upwards of 190,000 official fighters, not counting militia members who can be called upon to swell its ranks.
The Peshmerga also has a range of equipment dating from its time as a guerrilla force - as well as more modern U.S.-supplied weaponry. For more information on the Peshmerga and its capabilities, check out this 2005 masters' disertation by former intelligence officer Michael G. Lortz.