The purpose with this paper is to analyze the temporal scope of the doctrine of Unwilling or Unable and focus on when the right to use force in self-defense ends. According to the doctrine a State has a right to use force in self-defense towards a non-state actor on another States territory, if the harboring state is Unwilling or Unable to suppress the non-state actor. This paper will first analyze which factors governs the right to use force in self-defense according to the Unwilling or Unable doctrine and secondly the findings will be applied to the situation in Syria, where the United States are using force in collective self-defense on Iraq’s request, towards ISIL. The conflict will be analyzed in three different time periods, 2014, 2016 and 2018 to identify for how long the United States has a right to use force in self-defense in Syria. The conclusion in this paper is that in 2014 and 2016 the United States has a right to use force in self-defense towards ISIL on Syria’s territory according to the doctrine, but in 2018 the circumstances has changed and the United States’ right to use force in self-defense in Syria has ended.