On the other hand, the SDF became one of the United States' main Syrian partners in the military intervention against ISIL, leading to U.S. troops being stationed along SDF-held territories, thus preventing a Turkish invasion.[6][7] At the same time, US President Donald Trump has expressed his intention to disengage from the Syrian Civil War, initially ordering all US personnel in Syria to be withdrawn,[8] before later deciding to leave a small contingent, at the behest of his military advisors.[9] Nonetheless, the US is keen on maintaining good relations with Turkey, which had by that point already been strained by the refusal of the US to extradite Turkish dissident Fethullah Gülen (whom Turkey accuses of masterminding the 2016 Turkish coup d'état attempt) and the Turkish purchase of S-400 missile systems from Russia,[10] as Turkey is considered NATO's key member in the Middle East.[11][12]