Simona Foltyn:

For four years, the Emergency Response Division, or ERD – together with other Iraqi ground troops and support from the us – fought and appeared to win a grueling war against ISIS, but the terror group has risen again…At the nexus of four provinces – Kirkuk, Salahuddin, Diyala and Sulaimania.

It's an area home to strategic roads, oil fields and several mountain ranges, which provide a sanctuary for the militants.

These coalition-trained troops are battle-hardened from having fought a mostly conventional war against ISIS. During the four-year conflict, the US supported the ERD with tactical advice, even though the unit had been banned from receiving military aid due to human rights abuses.

ERD commanders say their troops have benefited from that advice, but their enemy operates differently now. Returning to its insurgent roots, ISIS avoids large deployments that are easily seen from miles away. The troops struggle to spot their targets.