Her son, Seth, 10, who had moved in with his grandfather, switching towns and schools, was angry and depressed. His grades had plummeted and his weight had ballooned by 60 pounds. Her 4-year-old daughter, Celeste, scarcely knew her. And in Specialist Holschlag’s absence, new rules had taken hold — chocolate syrup on waffles, Mountain Dew with dinner. Any hint of a return to the old order met with tirades and tantrums.

Specialist Holschlag, a single mother and a combat medic, had changed profoundly, too. The violence in Ramadi had staked a claim on her patience, her tenderness and her resilience. She snapped at her children routinely, at times harshly. ...