Thaier Al-Sudani/REUTERS
The Kurdish forces, known as Peshmerga, have proven themselves to be the most effective bulwark so far against ISIS's blitz. The Peshmerga, whose name is Kurdish for "those who face death," have helped to limit ISIS's incursions towards Baghdad from the north. At the same time, the Kurds have also seized oil-rich Kirkuk, known as the "Kurdish Jerusalem," which is formally outside of the autonomous Kurdish Region in Iraq.
The Peshmerga's numbers, dedication, and discipline make them possibly the strongest fighting force in Iraq.