See J. T. Strate, Post-Military Coup Strategy in Uganda: Amin's Early Attempts to Consolidate Political Support in Africa (1973), H. Kyemba, A State of Blood (1977), D. Barnett and R. Wooding, Uganda Holocaust (1980), and P. A. Allen, Interesting Times: Life in Uganda under Idi Amin (2000); B. Schroeder, dir., General Idi Amin Dada (documentary film, 1976; video, 2002).
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Muhammad ibn Jarir al-Tabari records that Harun al-Rashid several times impressed on his sons they should respect each other and honour the succession as Harun arranged it. In A.H. 186, Harun had al-Amin and al-Ma'mun sign pledges during a pilgrimage to Mecca that both would honour his will. Al-Amin, would receive the Caliphate and al-Ma'mun would become governor of Khurasan in eastern Iran and would furthermore be granted almost complete autonomy. On al-Amin's death, according to Harun's decision, al-Ma'mun would become Caliph.
The brothers had different mothers. Al-Amin was prompted to move against al-Ma'mun by meddlesome ministers, especially al Fadl ibn ar Rabi. Al-Amin had Harun's succession documents brought from Mecca to Baghdad, where he destroyed them. Al-Amin sent agents east to stir opposition to al-Ma'mun. However, a careful watch at the frontier denied these the opportunity. Al-Amin denied al-Ma'mun's request for his family and money and kept them in Baghdad.Ali ibn Isa ibn Mahan against Al-Ma'mun. Ali advanced on Rayy. Ma'mun's capable general Tahir bin Husain met and defeated Ali who was killed.
Al-Amin faced an uprising in Baghdad led by Ali ibn Isa's son Husayn. This was quelled and Husayn was killed. Tahir took Ahwaz and gained control of Bahrayn and parts of Arabia. Basra and Kufa swore allegiance to al-Ma'mun. Tahir advanced on Baghdad and defeated a force sent against him. In Mecca, Dawud ibn Isa reminded worshippers that al-Amin had destroyed Harun ar Rashid's succession pledges and led them in swearing allegiance to al-Mamun. Dawud then went to Marv and presented himself to al-Ma'mun. Al-Ma'mun confirmed Dawud in his governorship of Mecca and Medina.
Tahir advanced and set up camp near the Anbar Gate. Baghdad was besieged. The effects of this siege were made more intense by the rampaging prisoners who broke out of jail. There were several vicious battles, such as at al-Amin's palace of Qasr Halih, at Darb al- Hijarah and al-Shammasiyyah Gate. In that last one Tahir led reinforcements to regain positions lost by another officer. Overall the situation was worsening for al-Amin and he became depressed.
When Tahir pushed into the city, al-Amin sought to negotiate safe passage out. Tahir reluctantly agreed on the condition al-Amin turn over his sceptre, seal and other signs of being caliph. Al-Amin tried to leave on a boat, apparently with these indications he was caliph. He rejected warnings he should wait. Tahir noticed the boat. Al-Amin was thrown into the water, swam to shore, was captured and brought to a room where he was executed. His head was placed on the Anbar Gate. Al-Tabari (v. 31 pp. 197-202) quotes Tahir's letter to al-Ma'mun informing that caliph of al-Amin's capture and execution and the state of peace resulting in Baghdad.