Thereafter, there rose another cry for revenge for the blood of Uthman, this time by Mu'awiya, kinsman of Uthman and governor of the province of Syria. However, it is regarded more as an attempt by Mu'awiya to assume the caliphate, rather than to take revenge for Uthman's murder. Ali fought Mu'awiya's forces to a stalemate at the Battle of Siffin, and then lost a controversial arbitration that ended with the arbiter, 'Amr ibn al-'As, pronouncing his support for Mu'awiya. After this Ali was forced to fight the Battle of Nahrawan against the rebellious Kharijites, a faction of his former supporters who, as a result of their dissatisfaction with the arbitration, opposed both Ali and Mu'awiya. Weakened by this internal rebellion and a lack of popular support in many provinces, Ali's forces lost control over most of the caliphate's territory to Mu'awiya while large sections of the empire—such as Sicily, North Africa, the coastal areas of Spain and some forts in Anatolia—were also lost to outside empires.