The Abbasid leadership had to work hard in the last half of the 8th century (750–800) under several competent caliphs and their viziers to usher in the administrative changes needed to keep order of the political challenges created by the far-flung nature of the empire, and the limited communication across it.
It was also during this early period of the dynasty, in particular during the governance of al-Mansur, Harun al-Rashid, and al-Ma'mun, that its reputation and power was created.

Al-Mahdi restarted the fighting with the Byzantines, and his sons continued the conflict until Empress Irene pushed for peace.
After several years of peace, Nikephoros I broke the treaty, then fended off multiple incursions during the first decade of the 9th century.
These attacks pushed into the Taurus Mountains, culminating with a victory at the Battle of Krasos and the massive invasion of 806, led by Rashid himself.

Rashid's navy also proved successful, taking Cyprus.
Rashid decided to focus on the rebellion of Rafi ibn al-Layth in Khorasan and died while there.
Military operations by the caliphate were minimal while the Byzantine Empire was fighting Abbasid rule in Syria and Anatolia, with focus shifting primarily to internal matters; Abbasid governors exerted greater autonomy and, using this increasing power, began to make their positions hereditary.

At the same time, the Abbasids faced challenges closer to home.
Harun al-Rashid turned on and killed most of the Barmakids, a Persian family that had grown significantly in administrative power.
During the same period, several factions began either to leave the empire for other lands or to take control of distant parts of the empire.
Still, the reigns of al-Rashid and his sons were considered to be the apex of the Abbasids.

After Rashid's death, the empire was split by a civil war between the caliph al-Amin and his brother al-Ma'mun, who had the support of Khorasan.
This war ended with a two-year siege of Baghdad and the eventual death of al-Amin in 813.
Al-Ma'mun ruled for 20 years of relative calm interspersed with a rebellion in Azerbaijan by the Khurramites, which was supported by the Byzantines.
Al-Ma'mun was also responsible for the creation of an autonomous Khorasan, and the continued repulsing of Byzantine forays.

Al-Mu'tasim gained power in 833 and his rule marked the end of the strong caliphs.
He strengthened his personal army with Turkish mercenaries and promptly restarted the war with the Byzantines.
Though his attempt to seize Constantinople failed when his fleet was destroyed by a storm, his military excursions were generally successful, culminating with a resounding victory in the Sack of Amorium.
The Byzantines responded by sacking Damietta in Egypt, and Al-Mutawakkil responded by sending his troops into Anatolia again, sacking and marauding until they were eventually annihilated in 863.
The Abbasid leadership had to work hard in the last half of the 8th century (750–800) under several competent caliphs and their viziers to usher in the administrative changes needed to keep order of the political challenges created by the far-flung nature of the empire, and the limited communication across it. It was also during this early period of the dynasty, in particular during the governance of al-Mansur, Harun al-Rashid, and al-Ma'mun, that its reputation and power was created.
Al-Mahdi restarted the fighting with the Byzantines, and his sons continued the conflict until Empress Irene pushed for peace. After several years of peace, Nikephoros I broke the treaty, then fended off multiple incursions during the first decade of the 9th century. These attacks pushed into the Taurus Mountains, culminating with a victory at the Battle of Krasos and the massive invasion of 806, led by Rashid himself.
Rashid's navy also proved successful, taking Cyprus. Rashid decided to focus on the rebellion of Rafi ibn al-Layth in Khorasan and died while there. Military operations by the caliphate were minimal while the Byzantine Empire was fighting Abbasid rule in Syria and Anatolia, with focus shifting primarily to internal matters; Abbasid governors exerted greater autonomy and, using this increasing power, began to make their positions hereditary.
At the same time, the Abbasids faced challenges closer to home. Harun al-Rashid turned on and killed most of the Barmakids, a Persian family that had grown significantly in administrative power. During the same period, several factions began either to leave the empire for other lands or to take control of distant parts of the empire. Still, the reigns of al-Rashid and his sons were considered to be the apex of the Abbasids.
After Rashid's death, the empire was split by a civil war between the caliph al-Amin and his brother al-Ma'mun, who had the support of Khorasan. This war ended with a two-year siege of Baghdad and the eventual death of al-Amin in 813. Al-Ma'mun ruled for 20 years of relative calm interspersed with a rebellion in Azerbaijan by the Khurramites, which was supported by the Byzantines. Al-Ma'mun was also responsible for the creation of an autonomous Khorasan, and the continued repulsing of Byzantine forays.
Al-Mu'tasim gained power in 833 and his rule marked the end of the strong caliphs. He strengthened his personal army with Turkish mercenaries and promptly restarted the war with the Byzantines. Though his attempt to seize Constantinople failed when his fleet was destroyed by a storm, his military excursions were generally successful, culminating with a resounding victory in the Sack of Amorium. The Byzantines responded by sacking Damietta in Egypt, and Al-Mutawakkil responded by sending his troops into Anatolia again, sacking and marauding until they were eventually annihilated in 863.
Abbasid Caliphate