Imam Jawad’s (A.S.)seventeen years of Imamate coincided with the reigns of Ma’mun and Mu’tasim Abbasi, two of Abbasid Caliphs: 15 years in the reign of Ma’mun(1) and two years in the reign of Mu’tasim. During this period the Imam experienced great hardship in preaching Shiism. Ma’mun’s reign was especially hard on the Imam for as Ibn Nadim has said: “Ma’mun was the most knowledgeable of the caliphs in jurisprudence and theology.” Imam Jawad’s (A.S.)first fifteen years were similar to that of his father in that he was forced to deal with the most knowledgeable and deceitful Abbasid Caliph.
When Ma’mun entered Baghdad in the year 204 A.H, he ordered for Imam Jawad (A.S.) who according to some narrations was ten years old at the time, to move to Baghdad so that he could suppress Imam Jawad (A.S.)just as he had done so to his father, Imam Reza (A.S.).
Ma’mun was accused for the murder of Imam Reza (A.S.) further he greatly feared the Shiites and the Muslims’ affection toward the Ahl al-Bayt (A.S.). Thus by marrying his daughter, Umm al-Fazl, to Imam Jawad (A.S.) he not only wanted to set himself free from these fears and accusations, but to also strengthen the basis of his government by putting on a false facade of being a devotee of the Ahl al-Bayt (A.S.).
Imam Jawad (A.S.) saw his situation like that of his father, and agreed to his marriage with Umm al-Fazl. Little however did Ma’mun know that this act of the Imam actually destroyed Ma’mun’s plans of killing Imam Jawad (A.S.) and his followers. The Imam, who was fully aware of Ma’mun’s political ambitions and plans of taking advantage of his political and religious position in society, refused to remain in Baghdad and returned to Madinah.
Umm al-Fazl’s letters to his father about Imam Jawad’s (A.S.)lack of attention toward her, and her not having a child from the Imam are clear proof to the fact that this marriage was a forced marriage upon the Imam. For, Ma’mun had planned that by receiving a grandchild from the Imam and Umm al-Fazl, he would have taken advantage of the child’s lineage and refers to him as the grandson of Prophet Muhammad (S.A.W.). He would have then used this title to strengthen future movements of the Abbasid Dynasty.
In the year 218 A.H. Ma’mun passed away on his way to war with Rome. Despite the military forces of the Abbasid dynasty’s desire to pay allegiance to Abbas, the son of Ma’mun, instead Abbas acted according to the will of his father and paid allegiance to his uncle, Mu’tasim.
Mu’tasim, the eight Abbasid Caliph, ordered for Imam Jawad (A.S.) to move from Madinah back to Baghdad. The Imam had not choice, and so upon introducing his son, Imam Hadi (A.S.) as his successor, Imam Jawad (A.S.) went to Baghdad with his wife Umm al-Fazl.
Mu’tasim’s character differed greatly from Ma’mun’s for Mu’tasim had a military attitude, and lacked the insight and knowledge of Ma’mun. He did not have Ma’mun’s art in treachery, and thus acted in an opposite manner toward the Ahl al-Bayt (A.S.), making his true face apparent amongst the people.
In the last two years of Imam Jawad’s (A.S.) life, the Imam was therefore under an even more severe surveillance by the military forces of Mu’tasim. Yet despite this restraint, the Imam would prove his Imamate to others through his presence in scholarly and scientific debates and through his gifted powers and generosities.
Apart from all said, Mu’tasim would continue to devise plans for murdering Imam Jawad (A.S.). Allamah Majlisi records on the martyrdom of Imam Jawad (A.S.) that Mu’tasim ordered the Imam’s wife Umm al-Fazl to poison him. Mu’tasim, who was aware of the Imam’s interest in Arabian Jasmine grapes, poisoned the grapes and gave them to Umm al-Fazl who gave them to the Imam.(2) And, it was upon such that the Imam was martyred at the age of twenty five.
 

Footnotes:
1. From the year 203 A.H, the martyrdom of Imam Reza (A.S.) until the death of Ma’mun in the year 218 A.H.
2. Bihar al-Anwar, vol. 50, p. 17