After signing the treaty, Imam Hasan [a], the grandson of the Holy Prophet [s], remained in Kufa for a few days. His heart was wrung by pain for what had happened. He prepared to return to Madina, the city of his illustrious grandfather, the Messenger of Allah [s].
When his noble procession set out, all the people of Kufa went out. They were deeply remorseful, with the look of great sorrow on their faces. They were either in tears or sad-looking. And why not? They would be humiliated after Imam Hasan [a] and Ahlul Bayt had departed. The seditionists were by now in control of their lives, they appeared helpless, and disgrace descended upon their city.
Mu'awiyah transferred the caliphate and general command from Kufa to Damascus. The Umayyad military forces entered Kufa, tightening their grip on it, striking fear into the hearts, and spreading their terror. Those who collaborated with the Urnayyads were rewarded, and those who opposed them were put to the sword.
Imam Hasan's [a] caravan set off crossing the desert, while pain was striking at his heart, parting with his capital, and the places which held his memories. It was hard for him to abandon his Shi'ites and elite who supported him with firm determination and resolution, until they arrived at a blind alley. They were besieged and hunted down with the employment of every low and cheap method. The Umayyad clique began their vengeance.
On the other hand, when his caravan approached the holy city of Madina, its people rushed to welcome the Imam and his family [a]. Rapture coloured their faces. Why not?
The blessing of the presence of the Ahlul Bayt [a] had returned to them, and the goodness, all goodness, came to their city.
As soon as he settled, Imam Hasan [a] and his family set about to take up his religious responsibilities, but on a new line.
If he was a ruler before who discharged the affairs of the ummah, and set plans for its future through the office of political Imamate, and steered the ship to the coast of happiness, goodness and guidance; after the signing of the treaty he tread upon a new path.
He established a great ideological school and leadership so as to be a seat of guidance and knowledge by which the ummah would be guided to the straight path of Allah, and His concluding Message.
That school played an effective part in ripening public opinion, correcting its course, and saving it from the deviation of the official bodies led by Mu'awiyah bin Abu-Sufyan.
The school of Imam Hasan [a] gave fruit twofold. It graduated the greatest scholars and traditionalists, like Hasan al-Muthanna, al-Musayyab bin Najbah, Suwaid bin Ghaflah, al-Sha'bi, al-Asbagh bin Nubatah, Abu-Yahya al-Nakha'i, Ishaq bin Yasar, and others...
If Imam Hasan [a] had scored a great and glorious victory for Islam by establishing this school; he obliged the ummah and the Message another great favour. He called the people to uprightness of behaviour and faith, and the following of the Messenger [s] and his family [a], doing their best to spread good manners and fight every evil act.
Apart from this, he paid special attention to his society. He took care of the poor, the helpless and destitute. He looked after the needy. We cited some examples of his care of the poor previously.
Beside his ideological activities, it was only natural that Imam Hasan [a] would plan the future of his ummah, both in social and political spheres. In these fields, he took a good course for the benefit of the Divine Message and the ummah. He created an Islamic current of awareness among the ummah.
It became clear for the ummah that the legitimate Imamate was the right of Ahlul Bayt [a], and particularly Imam Hasan [a]. Mu'awiyah and the likes of him were not fit to rule. Obedience to them was incompatible with the pristine Islamic line. Imam Hasan [a], and the Muslim intellectuals who graduated from his school, succeeded in bringing about an ummah with a sharp political awareness. An ummah which opposed the Umayyad rule, in thought, course of action, and method, and which defended Islam throughout the next generations.
The Umayyad rule was not unaware of these nascent Islamic activities. It was they, as a matter of fact, who were to be reckoned with. That is why the high-ranking officials of the Umayyad government held a meeting to discuss the matter. The meeting was attended by, in addition to Mu'awiyah, Amru bin al-Aas, al-Walid bin Aqabah bin-Mu'eet, Utbah bin Abu-Sufyan and al-Maghirah bin Shu'bah!
They said to Mu'awiyah, in part: "Hasan has certainly animated his father and revived his memory. He talked and he said the truth, gave orders and was obeyed, and was followed by the people. Such thing would raise him to a higher level. Every time we hear from him something which does us harm..." 
This report, though brief, was the most dangerous report submitted by the chiefs of the Umayyad house and its leaders, to their chief, Mu'awiyah, about the activities of Imam Hasan [a].
The movement of Imam Hasan [a] gained strength, so much so that he left for Damascus, the capital of the Umayyads.
There he sat down with Mu'awiyah, explained to him the mistakes and schemes of the Umayyad rule, the superficiality of those in charge, and their diversion from the original Islamic line. His discussions there won him a lot of supporters and advocates. 
The fresh activities of Imam Hasan [a], and the new, historical mission which he shouldered to preserve the sound Islamic line among the people, made the Umayyad rule lose its head, and forge a hostile policy to get rid of the Imam [a] and his Islamic leadership.
The main ingredients of that policy were:
This is one of the most sad and enduring results of the Umayyad rule. So many false ahadith were introduced, first by the Umayyads and later by the Abbasids, that today, we Muslims of the 20th century have become so misguided by the lies which have remained in our ahadith and sunnah of our Prophet [s]. Surprisingly enough, the historians and narrators of hadith have not tried to eliminate and filter through these obvious lies. They continue to propagate them, confuse the ummah and misguide them to their own detriment. This is one of the main reasons that the Muslims of today remain weak and disunited.
Others were hushed by money also. A poet described this phenomenon in these two lines of verse:
"When a tongue criticises you, it is cut with dinars,
And when a conscience rocks you, it is shaken with a good official post."
Thus, Imam Hasan [a] went to meet his Lord, while standing in the fields of jihad, for the sake of Islam, which was preached by his father, the Commander of the Faithful, Imam Ali [a] and his grandfather, the Great Messenger of Allah [s].
Imam Hasan [a] attained martyrdom on the seventh day of the month of Safar (or the fifth or twentieth of the month of Rabi' al-Awwal in some reports), in the year 50 A.H.
He had asked his family, in his last will, to be buried by the side of his grandfather, the Messenger of Allah [s], but the Umayyads and the governor of Madina refused to allow his burial there. 
Ahlul Bayt [a] was thus forced to inter him at al-Baqi', by the side of his mother, Fatimah al-Zahra' [a].
Peace by upon you, Abu-Muhammad Hasan bin Ali, when you were alive, wronged, and dead.
 Tawfeeq Abu Alam, Ahlul-Bayt, p. 343, quoted from Sharh Nahj al-Balaghah.
 See: Hayat al-Imam Hasan [a] to be aquainted with those arguments, vol.2, p. 305 and the following pages.
 Muhammad Mahdi Shams al-Deen, Thawrat al-Husayn [a] (Revolution of Hussein [a],), (Beirut:1977) , 4th ed., p. 127.
 Bin Abi al-Hadeed says: "Abu Faraj says: 'Hasan [a] was laid to rest in the tomb of Fatimah, the daughter of the Messenger of Allah, [s], at al-Baqi'. He had expressed his desire in his last will, to be buried with the Prophet [s] but Marwan bin al-Hakim did not allow it. The tribe of Ummayad carried their weapons. Marwan said: 'O Lord! War is better than easy and comfortable life.'" See: Sharh Nahj al-Balaghah, (Egypt:1962), vol. 16, p. 50.