JANE FERGUSON:

This is where the battle for Mosul will begin.

Qayyarah, a small town just 35 miles south of Mosul, was occupied by ISIS until they were pushed out just over a month ago. Now some signs of life are returning. At the entrance to the town, a hand-painted sign reads: "Here is Qayyarah, the key to liberating Mosul."

ISIS set fire to Qayyarah oil wells in retreat.

This road is the front line before getting to ISIS-controlled Mosul, and all along the front line here, it is divided up between the various groups who are fighting ISIS. It represents just how complex the battle for Mosul will be.

U.S. Major General Gary Volesky, commander of the Army's 101st Airborne Division, knows the difficulties involved in getting Iraq's combative factions to work together.

"PBS NewsHour" traveled with the general to Qayyarah Air Field, destroyed by ISIS as they left here, he says. This will be the major hub, where U.S. support troops and Iraqi forces will work together as the offensive gets under way.

MAJ. GEN. GARY VOLESKY, Commander, 101st Airborne Division: All of the stakeholders recognize the importance of Mosul. I mean, we have been to meetings with both the Kurds, the Iraqis, a lot of the different stakeholders, if you will, and they all understand that they have got to come together to defeat Da'esh. And that's what they are doing.