The decline of the Abbasids was not a rapid and steady series of events. There were numerous revivals of the Caliphate in which some strong caliphs gained more control and influence over the Islamic world than their predecessors had. However, at no time after the death of Harun al-Rahid (reigned 786–809) was the Caliphate ever so powerful. This period is considered the golden age of the Abbasid Caliphate and was immediately followed by civil war between his sons. The two sons of Harun were called Al-Amin and Al-Mamun. Al-Amin was the eldest and was named heir to the Caliphate. However, Al-Mamun, who was the effective ruler of the eastern provinces, was ambitious. He was pushed to take over the Caliphate by his important advisor Al-Fadl. In 810 he declared himself an Iman, causing his brother's disinheritance and sending a large army to crush his ever-increasing rule over the Caliphate east of Baghdad. It seemed likely that Al-Mamun would be defeated. His army numbered around 4,000 men but faced 40,000. However he was fortunate in his commander, called Tahir bin Husain, who earned him a spectacular victory at Rayy in 811. Tahir proceeded to siege Baghdad in 812. In that year Al-Amin was captured and forced to hand over the position of Caliph to al-Mamun. Al-Amin was executed after attempting to flee Baghdad after it was captured. This war divided the Caliphate into factions and cost both sides a lot. As with most other occasions when a man usurps a throne, there are long-term repercussions and conflicts. Al-Mamun was plagued throughout much of his reign by rebellions. He fought for five years against an Alide rebellion that attempted to settle 'Al-Rida', or the... center of the paper...... ne of the Caliphate was the general economic recession. This had two main causes: first, the series of civil wars that engulfed the Caliphate, and second, the devastation brought to the agricultural heartland of Mesopotamia on which the Abbasids, as well as much of the Islamic world, depended. The demise of Iraqi agriculture was due both to the upheavals of war and to the chronic lack of state investment in recent decades. My final reason is the diversification of Islam. The Umayyad Caliphate remained strong for 200 years because Islam was confined to the elites. As Islam spread throughout the Caliphate's population, there was growing disenchantment within the old elites and an ever-increasing number of religious groups, sects, and factions that quarreled widely among themselves. Such disunity meant that a single Islamic nation could no longer exist.