His Caliphate
On the 21st night of the Ramadan of 40th Hijra Imam Ali (PBUH) passed away making all the people sorrowful and grieved. Imam Hassan (PBUH) who was 27 years of age came along with the people to the mosque and climbed the tribune and said, "Last night, a man, who was unique in knowledge piety, conduct and character among the previous ages people as well those to come in future, has gone out of you. He participated the battles along with the Prophet (PBUH) and strived hard to guard Islam. A person who was the thorn of the eyes of the enemies and the fruit of the heart of friends; and he did not spare and accumulate anything from the wealth of the world for himself, except for seven hundred dirhams by which he wanted to provide a servant for his family."
At this moment, the Imam (PBUH) wept bitterly and the people too wept. Then he spoke about himself. So that the people may know that the Imamate has been handed over to him and that people might not go astray and did not get misled. He said, "I am the son of the Prophet (PBUH), Ali (PBUH) and Fatima (PBUH). I am the flame of the lighted lamp of Prophet-hood; the family from which God has driven the dirt, contamination and pollution away.
Then Abdullah Bin-e-Abbas stood up and said "Oh people this is the son of the Prophet (PBUH) and your Imam, beware, that he is the right heir and successor of Ali (PBUH). So take the oath of allegiance and loyalty for him".
People moved in shape of groups towards Imam Hasan (PBUH) and took the oath of allegiance for him. Imam (PBUH) made it a condition that they would fight anyone against whom he fought and whenever he deemed it fit to make peace, they would also accept it. All of them accepted it, and willingly agreed and submitted to his Imamate.
The Conspiracies of Mu'awiyah
Mu"awiyah had established a government and dominion in Syria and for years he had played tricks with cunning ways and means against Ali (PBUH). He killed the friends of Ali (PBUH) and brought into existence the perverted group and sect of Khwaraj Now, when he heard that people, after the martyrdom of Ali (PBUH), took oath of allegiance to elect Imam Hasan (PBUH) for the caliphate post as the successor of the Prophet (P.B.U.H.). This thing was very hard for him to tolerate. He sent spies to Kufa andBasra to find out and get him informed about what was going on. And thereafter, they may plot and hatch conspiracies against Imam (PBUH) if they deem fit and suitable they might start subversion and sabotage and create chaos, and disorder.
Imam gave the order that the spies should be arrested and killed. Then he wrote a letter to Mu'awiyah:
"Oh Mu"awiyah! You send spies and set your hands upon subversion? I presume that you intend to fight a war and you like war. If it is so, then I am also ready for it and the war is at hand. Do wait.
Mu'awiyah! I am surprised over you that you are the candidate for a job, which you don't deserve and are not worthy for it. Neither you have any superiority in the religion nor have you left any good effect, mark or impression from yourself as a monument and memorial. Muslims have taken oath of allegiance for me (caliphate). It would be to the interest and benefit of Islam that you too accept this act (caliphate) like the rest of the Muslims. Oh Mu"awiyah! Do not move the untrue and illusive ahead, and you also take the oath and allegiance of faithfulness to me like the others, and do consider the blood of the Muslims respect worthy. If you do not accept my advice and wish to create disorder and chaos and spill the blood of Muslim I will quickly attack you along with the other Muslims, and will put you on trial."
Mu"awiyah in reply to the Imam wrote:
"In the same way as Abu-Bakr, due to his experience and expertise took the caliphate from Ali (PBUH), I am more deserving than you and have more experience and it is better that you be my follower so that you get the caliphate after myself, and I will give you, whatever is the income of Iraq."
Mu"awiyah not only denied and turned his face from taking the oath of allegiance, he also sent spies to Kufa to martyr the Imam. Thus the Imam (PBUH) had to wear armored Jacket under his clothes and then stand for offering the prayers. Once when one of the agents of Mu"awiyah threw an arrow towards him the arrow got ineffective due to the armored Jacket and so the Imam (PBUH) remained safe.
War Begins
It did not take long that Mu"awiyah, on the pretext of bringing into effect Islamic unity, gathered a huge army and mobilized it to fight the Imam in Iraq. When the news of the movement of Mu'awiyah"s army I reached the Imam, he invited the people to the mosque. He climbed the tribune and after the praise of God and the salutation to the holy Prophet (PBUH) said, "Mu'awiyah has moved towards Iraq along with his army. It is your turn to get ready for the war and defend your honor and religion." But those despicable, vanquished and comfort-loving people did not give a response to Imam (PBUH). Addi Bin Hatim stood up from among the people and very sadly addressed them saying, "What kind of people are you. What does this dead silence mean? Why do you not reply to the Imam (PBUH) and the son of your Prophet (PBUH)? Are you not afraid of abjectness and suffering? Be afraid of God's anger and torment and chastise and obey the order of your Imam (PBUH). Get up and manly press your weapon in your hands and defend your honor, respect and religion. So that the God and Imam (PBUH) are pleased with you.
These words alerted a group so they announced their readiness to take part in the battle. Addi Bin Hatim told Imam (PBUH), "We are ready and waiting for your order." Imam (PBUH) said, "I am proceeding towards the Nakheela Camp and whosoever is prepared and willing may go to that place, although I know that you will not practice upon your promise and Mu"awiyah will deceive you.
imam hassan
Disobeying the Imam (PBUH)
When Imam reached most of those who were shouting the slogans of "war, war" were not present there and had gone back and turned their back upon the promise they had made with him. Because those who had participated were comprised of:
1. Khawarij who had come to fight against Mu"awiyah and not for the sake of obeying the command of Imam (PBUH).
2. Those materialist and world adorers and greedy ones who were after the war booty.
3. Those who had participated for the sake of accompanying and following their tribal chiefs and not due to any religious inspiration.
This is the reason Imam (PBUH) addressed them saying, "You betrayed me, like you had betrayed my father, who was your Imam before me. I don't know whether you will fight siding with Imam or someone who absolutely does not believe in God and His Prophet (PBUH).
Then he selected a man named Hakam as the army commander and put four thousand men under his command so that he moves to the city of Ambaar and stays there and applies restraint to the forces of Mu'awiyah till getting further orders. But Mu'awiyah deceived him by giving him money and making false promises. And he joined his army along with his two hundred men.
Imam (PBUH) selected another man from the tribe of Bani Murad as his successor and said, "Although I do not have trust upon you. But this is a trial, you may also proceed."
When Mu"awiyah came to know about his arrival, he sent his delegates with five thousand dirhams for him and promised to give him a governorship. He was too deceived by Mu"awiyah and joined him.

Imam's Grief
When the news of the joining of tribal chiefs with Mu"awiyah reached the Imam (PBUH), he was much affected and shocked and said, "Did I not say several times that you do not have any faithfulness and trustworthiness, and your conduct with me is that of artifice, and cunningness? He then decided to gather an army himself and move. By the efforts of his friends nearly four thousand men gathered. Imam (PBUH) along with "Sabaat" went to Madayan and sent twelve thousand men under the command of Obaidullah bin Abbas and his helper Qays bin Saad, as a file leader and fore runner to meet and resist Mu'awiyah, so as to test their spirit and strength of devotedness. Mu"awiyah sent his agents along with one million Dirhams among the forces of Imam (PBUH) to get Qays deceived but Qays did not yield to his desire and answered them, "tell Mu"awiyah you cannot take my faith from me and I will not desert and leave Imam by any of your artifices and frauds."
The agents who got disappointed by Qays and went towards the real Commander Obaidullah bin Abbas and lured and deceived him, so he along with a group of his followers joined Mu"awiyah at the nighttime. When the army men of Imam (PBUH) became commander less, Qais took over the Command and lead the Jama'at prayers. Qays was fighting fiercely and ferociously and had made Mu"awiyah harassed and fearful. As a result, he sent a few spies among the army men of Qays, so that they may make this propaganda that Imam Hasan (PBUH) has entered into peace treaty with Mu"awiyah and you are fighting for no reason. By this way Mu"awiyah succeeded in separating and detaching the group of Khawarij from the Imam"s forces and in deceiving them to attack the Imam (PBUH) and what he desired did materialize.
The Rioter Khawarij
This stupid and silly group did believe in what spies of Mu"awiyah told them and disobeyed the orders of Imam (PBUH) and they raised a hew and cry that Imam Hasan (PBUH) had also become an infidel like his father (Maaz-Allah) and had joined hand with Mu'awiyah. Suddenly, a platoon attacked the tent of Imam (PBUH) and looted whatever they found, to the extent that they even pulled out the carpet of Imam (PBUH) from beneath him.
Imam (PBUH) was forced to leave that place and he rode upon horse and a group of his friends were all around him. One of them (the attackers) rushed out of his hiding place and injured the Imam (PBUH). Imam (PBUH) was carried to one of his friend's house and provided medical care and treatment. It came to it, that most of his governors, secretly and confidentially, wrote letters to Mu'awiyah saying we are at your command and disposal as soon as possible come to Iraq, we will arrest the Imam (PBUH) and hand him over to you. Mu'awiyah sent all those letters to Imam (PBUH) along with a covering letter saying, "These people did not remain faithful to your father and they will not remain on your side either. I am ready to sign a pact with you and overlook the war.
imam hassan

Why Imam (PBUH) accepted the Truce?
The adventurer Khawarij and the dishonest friends of Imam (PBUH) made it inevitable for the Imam (PBUH) to accept truce with Mu'awiyah. But truce did not mean that Imam (PBUH) colluded and put up with Mu'awiyah and agreed to his cruel and brutal activities. But it meant to make a no war pact with Mu'awiyah for a certain period. Because, if Mu"awiyah became victorious, he would had smashed and destroyed all the hopes of Islam and would have destroyed the foundation of Islam and killed all the true Muslims. Besides, the Roman Empire was seeking a chance to attack the Islamic lands, and this mutual difference of Muslims was the best opportunity for it. Thus Imam (PBUH) who was smoldering with pain spoke to his untrue and unfaithful friends, "I know that you would practice craftiness and artifice, a group who do not have neither shame nor religion have unconditionally handed themselves over to Mu'awiyah , woe to you, By God, Mu"awiyah will not fulfill his commitments. I wanted to establish for you the religion of the right but you did not help me. You started moving on the path of opposition and confrontation and committed dishonesty with me, which forced and obliged me to sign the treaty. By God, if I had friends and helpers I would not have surrendered the work to Mu"awiyah because, I consider the caliphate to be prohibited for Bani Ommayad. You will soon taste the bitterness of the conduct of Mu"awiyah, day and night. After the Imam (PBUH) was forced to make truce with Mu"awiyah, he wrote a letter to him saying, "I wanted to revive the right and put an end to rescind and vanity and establish the ruler ship of God and the sunnah of the Prophet (P.B.U.H.) but people did not agree and accompany me. Now, I am making a truce with you upon the conditions, which I know that you will not fulfill and comply with. But soon you would repent, but that will be a time when it will not be of benefit to you.
Then, he sent his cousin Abdullah Bin Harris to see Mu'awiyah so that he should get him committed upon the conditions, which he had presented after a negotiation with him, and write down the agreement, and treaty of truce.
A part of the truce treaty is as under: -
1. The blood of the Shi"as must remain respect worthy and their rights must not be confiscated and crushed.
2. Filthy language must not be used against Ali (PBUH) and his Shi"as.
3. Mu"awiyah should practice upon the Book of God (The Qur'an) and the Sunnah of Holy Prophet (PBUH).
4. The friends and companions of Imam (PBUH) must remain safe and secure from his mischief and brutalities wherever they live and no one has the right to resist them.
5. Imam (PBUH) does not call Mu'awiyah, The Commander of Faithful and will not take his name in the sermons.
6. Mu'awiyah must not hand over the caliphate to anybody after himself.

The Breaking of the Pact
After the peace pact was conducted, Mu"awiyah focused his attention upon Kufa and held the Jum'a prayer congregation at Nakheela. He evidently and clearly said in his speech "Oh people I did not fight against you so that you should offer your prayers and keep fast, instead, it was for the reason that I rule over you although you do not like it. I will crush all the conditions of truce pact conducted with Hasan bin Ali (PBUH) under my feet. But the conduct of Mu"awiyah in certain matters showed that he was strongly embarrassed and harassed due to the influence of Imam (PBUH) so that sometimes he was obliged to put into practice few of the points of the peace pact.
So that once when Bin Ziad the governor of Kufa followed and chased (to punish) one of the friends of Imam (PBUH), Imam wrote about the incident to Mu"awiyah, who at once reprimanded Bin Ziad about this event.
Finally Mu'awiyah Decided to make Yazeed, his son, his successor.
But the pact, which he had signed with Imam Hasan (PBUH), stopped him from this act. He decided to poison the Imam (PBUH) so that the way to the succession of his son Yazeed should become open and clear. And then make the people forcibly take oath of allegiance (for Yazeed's). Therefore, he contacted "Jaada" the wife of Imam (PBUH) and deceived by luring her and sent a poison for her, with the message that if you make your husband take this poison you will get a prize of one hundred thousand Dirhams from me. Besides, I will select you as the wife of Yazeed and you will become the wife of the caliph of Muslims.

Source: sahartv