A modern army without supplies is a dead army.
This map of our bases in Iraq is interesting.
Note how our bases extend even to the south along key points in the supply line that runs from Kuwaiti ports to our most northern units. And we have only outposts out toward the Iranian border so our supply lines aren't immediately vulnerable to an Iranian lunge across the border.
So when some clueless advocates of retreat from the fight in Iraq say we should boldly pull back into the Kurdish regions, please ask how we will supply those units in the landlocked Kurdish provinces without the bases that run through Iraq all the way to the Kurdish border to secure those supply lines.
And no, "I dunno" is not an adequate answer.
The United States Army in a hypothetical Kurdistan alone is an army without supplies.