In June 2014, a nihilistic terrorist group whose members thought nothing of decapitating their prisoners, massacring Shia and Christian Iraqis, and enslaving Yazidi women, drove the United States-funded Iraqi army out of the country’s second biggest city. Tens of thousands of Iraqi soldiers dropped everything U.S. taxpayers provided, including $1 billion in Humvees, and beat a path away from the Islamic State invaders.