This paper examines how non-state organized armed groups operating in areas of problematic sovereignty challenges existing Law of War. First, the initial phase of war is discussed. When a state is attacked by an organized armed group, based on another state, complex questions as to the territorial state's responsibility for the attack and the scope of the attacked state's right to self-defense arise. Secondly, a glance into the law regulating the conduct of hostilities reveals problems arising from a failure to take defensive measures to protect the population in these areas against the effects of attacks. Finally, the paper elaborates on attributes of non-state organized armed groups that affect the possibility of determining an end to the armed conflict. The legal analysis is illustrated by case studies from the Israeli experience.