What Happened The U.S. Department of Defense, reacting to reports that Turkey has been amassing troops along its border with northeastern Syria over the past several days, warned Ankara on July 13 against making any unilateral military moves into areas of Syria held by the U.S.-supported Syrian Democratic Forces (SDF). Why It Matters A Turkish military incursion into the SDF-controlled portions of Syria where U.S. troops also maintain a presence would deal another significant blow to U.S.-Turkish relations, not to mention raising the risk of an accidental clash between Turkish and U.S. forces. But there is reason to believe that Turkey wouldn't actually conduct such an operation at this time.