The second part or stage of the role of Imam Hasan [a] in the life of the Muslims commenced when his father appointed him as the next Imam. In the wake of the cruel attempt on his life by Abdul-Rahman bin Muljim and his cohorts, the dying Imam [a] said his last will to his son, Hasan [a]:
"...my son, the Messenger of Allah [s] ordered me to inform you of my last will, and hand over my books and weapons to you, exactly as he told me his last will and gave me his books and weapons. He ordered me to order you to give them to your brother, Husayn, when death approaches you..."
Then he turned to his son, Husayn, and said:
"And the Messenger of Allah [s] ordered you to hand them to this son of yours."
Thereupon, he took hold of the hand of Ali bin Husayn [a] and said to him:
"And the Messenger of Allah [s] ordered you to give them to your son, Muhammad bin Ali. Remember, the Messenger of Allah [s] and me to him."
Then he named as the witnesses to his last will, Husayn, his son Muhammad, all of his sons, and the chiefs and leading men of his Shi'ites (followers).
The last days of Imam Ali [a] teemed with many of his moral guidelines, which were aimed at establishing the right, and sticking to it. Most of them were addressed to his sons and particularly to Imam Hasan [a]. He emphasized his son's Caliphate and Imamate after him.
Shortly after the passing away of Imam Ali [a], the people of Kufa hurried to the mosque, dumbfounded and shocked at that great adversity. The grandson of the Messenger of Allah [s], Imam Hasan [a], stood amid this multitude, promulgating the first of his communiqués, after the departure of his great leader. He said:
"...this night, a man has died whom the first Muslims did not outrun with good deeds, nor did the last ones catch up with him in pleasing acts. He used to fight by the side of the Messenger of Allah [s], risking his own life for the sake of the Prophet's. The Messenger of Allah [s] would send him as his standard-bearer. Jibra'il would protect him by fighting on his right, and Mika'il on his left. He would not return from the battlefield until Allah had given him victory. He died in this night, on which Isa bin Maryam [a] ascended to heaven, and Yusha' bin Noon, the trustee of Musa [a], passed away. He has left no dirhams or dinars besides the 700 Dirhams which were left over from his pay."
At this point Imam Hasan [a] halted his speech for his tears choked him. The image of the great departing man, with his eternal deeds and stances, loomed before his eyes. The Muslims could not help crying bitterly with him. Then he resumed his speech. He said:
"O people! Who has recognized me, that is that. Who has not, let him know that I am Hasan bin Ali. I am the son of the Holy Prophet. I am the son of the Trustee. I am the son of the bearer of the good news, and the warner. I am the son of the Caller to Allah by His permission. I am the son of the bright lamp. I am from the house at which Jibra'il used to descend to us, and ascend from us, and from the Ahlul Bayt whom Allah kept away from uncleanness and totally purified them. I am from a household whose love Allah made an obligation on every Muslim. Allah, the Blessed and the Most High, said to His Prophet:
'...say: I do not ask of you any reward for it but love for my near relatives;...'"
Holy Qur'an (42:23)
Imam Hasan [a] concluded his speech by saying, 'Doing a good deed means loving us, the Ahlul Bayt.'
In this speech, Imam Hasan [a] spelled out the qualities of the late leader. Also he presented his own qualifications and stature in the Muslim world, and asserted the fact that he, and not any other person, was entitled to be the next leader of the Muslims.
No sooner did Imam Hasan [a] wind up his speech, than Bin Abbas rose to his feet urging the people to give their pledge of allegiance to the new Imam. And that was exactly what the people did.
Imam Hasan [a] received the pledge of allegiance from the people, and was acknowledged as the caliph and the ruler of Kufa, and later of the other Muslim cities. The news of the demise of Imam Ali [a] and the passing of the caliphate to his son, the grandson of the Messenger of Allah [s], soon spread.
Mu'awiyah rejoiced at the death of Ali [a]. His capital witnessed noisy festivals. Happiness flooded it! On the other hand, Mu'awiyah was greatly shaken by the announcement of Imam Hasan [a] as the new caliph, and at the pledge of allegiance which he had received. He sent for his advisors, and his leading men. They got together in an emergency meeting at his palace to discuss the latest developments and draw the policy which they would adopt in challenging Imam Hasan [a]. The participants decided to send spies to the Muslim community, under the rule of Imam Hasan [a] to frighten the people and float rumours against the rule of Ahlul Bayt [a], to the interest of the Syrian sedition.
Meanwhile the Umayyad party was busy winning over the leadership and the influential chiefs, who could influence the course of events in Iraq to the advantage of the Umayyad rule. They were generous in bribery, promising the people good rewards, presenting gifts to them, threatening them...and so on.
Mu'awiyah lost no time in implementing the resolutions of the meeting. He set up a network of spies, and appointed two men to surprise them. One of them was named Humairi. He made for Kufa. The other was called Qeeni. He headed for Basrah... 
Imam Hasan's [a] plans of solidifying the government system, and establishing it on a firm ground, were soon effective in unearthing the plots of the Umayyads.
In the wake of that, Imam Hasan [a] sent a letter to Mu'awiyah warning him, and threatening him with war:
"...Mind you. You have sent stealthily men to me. It is as if you like to go to war. I have no doubt about it. Then anticipate it, Allah willing. I have heard that you rejoiced about what the wise men do not gloat over. Your parable is like the one of whom the poet says: "I and the one who had died are like someone who goes home, goes to sleep, to wake up the following day. So, tell him who remains behind that who departs: 'Prepare for something like this. You, too, will be something of the past.'"
Mu'awiyah, in a responding letter, dodged and denied that he had rejoiced at the death of Imam Ali [a], something which we will not discuss in length here. They exchanged letters. The most important of the letters was that which was sent by Imam Hasan [a] in which he called on Mu'awiyah to stop opposing him and submit to him as he was the legitimate leader. Tension heightened between the two parties, so much so, that Mu'awiyah wrote a letter in which he called on Imam Hasan [a] to abdicate and join him, with the promise that the caliphate would be his after Mu'awiyah's death!
Imam Hasan [a] sent a short letter which displayed his insistence and determination:
"Mind you, your letter has arrived. You mention in it what you mention and I did not answer you...I take refuge with Allah from that. Follow the right, you will know that I am its follower. I will be a sinner if I tell a lie. And peace be upon you."
That was the last letter. The situation went from bad to worst. War was declared between the two parties.
Mu'awiyah was the first to declare the state of war. He began to advance his armies towards Iraq. The Muslims communicated the news of Mu'awiyah's move to one another. Imam Hasan [a] took due measures to face the coming enemy.
Imam Hasan [a] announced, in a statement, the next move. He called the ummah to mobolize and prepare for war:
"Mind you, Allah ordained jihad on His creatures, and made it a duty which they receive reluctantly. Then He said to the combatants; 'Be patient, Allah is certainly with the patient.' You, O people, will not win what you love without enduring what you do not like. Go out, may Allah have mercy on you, to your camp at al-Nukhailah, till we think and you think, and see and you see."
It brings excruciating pain to know that the multitudes of people who listened to the statement of Imam Hasan [a] were susceptible to the Umayyad rumours and lies.
Instead of preparing themselves to defend the clear right, they were shocked and flustered. They responded coldly to the statement of their Imam. They did not accept his call to prepare for war and shoulder their responsibilities.
Some of the people were resigned to the status quo and they appeared drawn to life. Others were lured into apathy by Umayyad money. Imam Hasan [a] was disappointed when he saw the true feeling of the masses which he led, and in which he saw the base on which he was depending to ward of the dangers encircling the Islamic message because of the hostile activities of the Umayyad party.
Those listless multitudes were stolid. They lost their vitality because of only a slight shock. It was because of their weak faith. The followers of the Imam [a] were unaware of their historical responsibility to keep the Divine Message intact and keep it safe from sedition. They were oblivious to the line of Imamate represented by Imam Hasan [a], and to the fact that they should obey him and defend him because he was the actual representative of the same Islam which was revealed to the Messenger of Allah [s].
Amid those stunned, defeated lumps of people, the call of the few faithful of Islam and the true committed men who attached themselves to Ahlul Bayt [a], thundered. They expressed their deep loyalty. They reproached those cowardly multitudes, and spoke their minds uncompromisingly and daringly.
At the top of the list of those faithful, pious men were: Uday bin Hatim, Qais bin S'ad bin Ubadah, Ma'qal bin Qais, and Ziyad bin Sa'sa'ah al-Timeemi. 
They scolded, reprimanded and urged the people to take on their religious responsibility. At the same time they did not forget their Imam [a]. They took his hand and made a pledge to march forward in support of right and face tyranny and sedition fearlessly until they achieved martyrdom or victory.
Imam Hasan [a] praised them for their true stance, and addressed them in these words:
"You are truthful, may Allah have mercy on you. I still know of your true intention and loyalty, your approval and true love. May Allah reward you the best of rewards."
The committed people hastened to al-Nukhailah and encamped there, in obedience to their Imam [a]. Imam Hasan [a], afterwards, followed them with an army, estimated by some historians, at 4,000 men.  The rest of the people were to join him.
Imam Hasan [a] hoped that the people would support the right cause and so come to defend Islam. But their delay in joining him made Imam Hasan [a] return once again to his capital, Kufa, to egg on the people to join him.
He marched on, leading a tremendous army, which was paradoxically in low spirit, eaten away by weakness and disharmony. He arrived in al-Nukhailah, where he organized his army, and set plans for the commanders of the divisions. From there, he headed for Dair Abdul-Rahman. There he decided to send a military force ahead of his army. He elected his cousin Ubaidullah bin al-Abbas as its commander. He said to him:
"...Cousinl I am sending with you twelve thousand men, among whom there are famous horsemen of the Arabs, and the Qur'anic reciters of Kufa. Each one of them is equal to one battalion in courage. March with them, be kind to them, look at them with a smiling face, be humble to them, and consult them. They are the remaining men whom the Commander of the Faithful [a] trusted. Lead them along the bank of Euphrates. Then march till you come face to face with the army of Mu'awiyah. If you meet him, keep him there till I join you. I will go, following you closely behind. Keep me informed of your moves on a daily basis. Consult these two men, Qais bin S'ad and Sa'eed bin Qais. If you meet Mu'awiyah, refrain from engaging him in battle till he fights you. Should he do so, then fight him. If you are injured or killed, Qais bin S'ad will succeed you as the commander of the army, and if he is injured or killed, Sa'eed bin Qais will succeed him."
The vanguard took its position at Maskin, on the banks of al-Dijail river in Iraq. The main army, under the command of Imam Hasan [a], encamped at Madhlam Sabat, near al-Mada'in.
It was not long before all the hitherto hidden ills came to the surface, in the forms of disunity, frailty, sedition, chaos, and conspiracy against the leadership itself. Imam Hasan [a] was pressured to sign a treaty with Mu'awiyah.
 See: Shaikh al-Tabarsi, Alam al-Wara, 3rd ed., p.206, and the following pages (Reports emphasising the Imamate of Hasan [a] quoted from al-Kafi). See also: Hayat al-Imam Hasan [a], vol, 1, p. 515, Kashf al-Ghummah fi Ma'rifat al-A'immah (Removing the Grief About the Knowledge About the Imams). vol. 2, p.155, al-Bihar (Seas). vol. 42, p.250, and others.
 A'lam al-Wara (Texts indicating the Imamate of Hasan), p.206 and the following pages. Al-Qarashi, Hayat Hasan bin Ali with a slight difference, vol.2, pp.31-32.
 Hayat al-Imam al-Hasan [a], vol.2, p.33.
 Al-Fusool al-Muhimmah, chapter of Hasan [a], p.135 and the following pages.
 Muhammad Jawad Fadhlullah, Sulh al-Imam al-Hasan (The Peaceful Agreement of Imam Hasan), 1973 ed., p.60.
 Tawfeeq Abu-Alam, Ahlul Bayt.
 Bin al-Hadeed, Sharh Nahj al-Balaghah (Commentaries on Nahj al-Balaghah), 1962 ed., vol.16, p.37.
 Ibid., p.38.
 Ibid., p.39.
 Al-Nukhailah is a place near Kufa in the direction of Syria.
 See footnotes of Hayat al-Imam Hasan, vol.2, p.72 and 1965 ed., quoted from al-Kharayij wa al-Jarayih, p.228, and Sharh Nahj al-Balaghah, vol.16, p.40.