Hussein Shehab knew things were going badly when he spotted the Iraqi police pickup trucks. They were flying the black flag of Islamic State fighters, who were driving the vehicles straight toward him and his fellow Iraqi security force soldiers.

It was June 9 in Mosul in northern Iraq. Shehab, a federal paramilitary police officer assigned to an army unit, realized that other officers had abandoned their vehicles and fled Islamic State fighters who were about to seize Iraq’s second-largest city.

By the end of the day, Shehab’s entire division had collapsed. Two army divisions also disintegrated as thousands of soldiers and police officers shed their uniforms, dropped their weapons and ran for their lives. Shehab, told that his commanders had deserted, tossed his rifle and ran away too. […]