The mainly Kurdish Syrian Democratic Council (SDC), which receives vital support from the United States and an estimated 2,000 special operations forces troops based in the northeast, made the unusual gesture on July 30 of returning to the Syrian army the remains of 44 soldiers who had been executed by the Islamic State in the village of Ain Issa in 2014. Ten days earlier, local officials had uncovered four mass graves near what had been the headquarters of the 93rd Brigade, and the Kurds used the occasion to help mend fences with President Bashar al Assad. The process of reintegrating the largest Kurdish-controlled region into the rest of Syria is underway, and the United States can do little to stop it....