WASHINGTON (AP) — U.S. teams of special forces going into Iraq after a three-year gap will face an aggressive insurgency, a splintering military and a precarious political situation as they help Iraqi security forces improve their ability to battle Sunni militants.

The Army Green Berets, expected to make up much of the U.S. force, have been assessing and training other militaries for decades as a core part of their job. But while much of what they will be doing in Iraq will be familiar, it will be complicated by the stunning collapse of the Iraqi military, left leaderless by internal Sunni-Shiite divisions.