U.S. and coalition troops were forced to allow hundreds of Islamic State commanders, fighters and their families to flee the embattled northern Syrian town of Manbij, fearing any attempt to attack the escaping forces would end in massive civilian casualties. A convoy of a “hundred to a couple of hundred” individuals associated with the Islamic State, also known as ISIS or ISIL, left Manbij Friday shortly after the Syrian Defense Forces, the American-backed paramilitary force battling the Islamic State in the country, wrested the city from the terrorist organization’s control, according to Col. Chris Garver, the top U.S. military spokesman...