Harun al-Rashid was the last 'Abbasid caliph to rule a clean-cut empire and after his death, the empire was divided in two. One son, Amin, got the western area and the caliphate, and his other son, Al-Mamun got the eastern area, the army, and the right to succession. Moreover, the 4th Fitna (811-813) was not about religious principles, but it was a civil war between Amin and Al-Mamun; Amin wanted his son to be the next caliph, but Al-Mamun didn't agree because Amin didn't have the right to succession. Al-Mamun entered present-day Baghdad in 819 and fought his brother/brother's empire with the assistance of Tahir, a Khurasani warlord. Once Al-Mamun won, he formed a new empire, give his former empire to Tahir (who in turn ruled the Tahirids, which lasted from 821-873). All of this has lead to a further breaking up of the empire and conflict within the caliphate. Besides, Al-Mamun attempted religious and political authority and he supported rational thought, which put him at odds with the ulama.
• What about the Third Crusade?
When the Mamluk general Imad-ed-din Zangi died, his son Nureddin, who added Damascus to the land his father had gathered, succeeded him and after the death of Nureddin in 1174 AD, a strong Kurdish general named Salah al-din took over. Salah al-din soon conquered Egypt from the Fatimids, and then he was strong enough to begin fighting the Christian kingdoms in Israel and Lebanon. In 1187, Salah al-din took Jerusalem. Moreover, the people of Europe were very upset and the pope urged the kings of Europe to unite against Salah al-din, and in the end Richard, the Lionhearted, the king of England, Philippe Augustus, the king of France, and Friedrich Barbarossa, king of Germany and Holy Roman Emperor, all went to Jerusalem. Beside, a special tax in both France and England raised money for the crusade. Nevertheless, the Third Crusade, like the Second, ran into a lot of