This study aims to reveal the manifestations long highlighted by some historical novels in different sources, and confirmed by the New-researchers about the nature of the civil war and the conflict between the two brothers. The researcher also aims to identify the personality of the caliph Al-Amin during the conflict, and the personality of Al-Maamun, as the crown prince, during the war, and the impact of political groups in this conflict. The study uses a historical analysis approach and the comparison between novels, relevant views related to the subject matter and the representation of the topic in a new manner through methods that are subjected to the scientific approach in historical research. This research was divided into an introduction that addresses the issue of succession in the Abbasid Empire until the reign of Harun al-Rasbid (132-170 AH / 749-808 AD), and examines previous studies and analysis of some of the main sources of direct relevance to the subject matter. It also contains four chapters and a conclusion that included the most important results that have been found in the study. Chapter one deal's with the policy of Harun al-Rashid in addressing succession and its impact on the political situation in the Abbasid Empire. While Chapter two focuses on the civil war (1): the diplomatic phase (193-195 AH / 808-811 AD) The resear touched upon the correspondence between Al-Amin and Al-Maamun and the role of power and political blocs in igniting the pace of war between them. The third chapter traces the armed confrontation (195-198 AH / 811-813 AD), dealing with the stages of military confrontation between Al-Amin and Al-Maamun ending with the death of Caliph al-Amin, while the fourth and last chapter deals with the consequences of the civil war. The researcher reached to many results, and among them most importantly was that the civil war, which lasted for five years, was nothing but a war between the political groups that took control of the Abbasid Caliphate led by the two Fadhls, Fadhl bin Rabi' and Fadhl bin Sahl, which had detrimental consequences to the Islamic Society and eventually affected the future of the Abbasid state.