How did Imam Ali (A.S) accept the offer of caliphate after twenty five years?

Imam Ali (AS), after twenty five years of exclusion from power, on the Helpers’ and Emigrants’ insistence, reluctantly accepted the offer of the Caliphate. It was a choice that would take its toll on him. Muhammad ibn Hanifa reports: ‘I was with my father when Uthman was killed. The Companions of the Prophet (PBUH) came to Ali’s (AS) house and called out altogether: “The man is slain. The people need a leader. And there is no one is better than you; there is none more experienced or learned in Islam than you, and you are the closest to the Prophet (PBUH).”

Imam(AS) demurred and said: “I am better as your advisor than your ruler.” However, they replied: “By God, we will not leave until we pledge allegiance to you.” Seeing that their minds were made up, the Imam stated: “The pledge should be given openly at a mosque and with the consensus of the Muslims.”’

Abdallah ibn Abbas reports: ‘I was so afraid that in the mosque some would turn against Ali (AS) and defy him but he would not accept anything but taking the oath at the mosque. In the Mosque, when Ali (AS) came in, both the Helpers and the Emigrants took the oath to him, then the rest of the people followed them and did the same thing.’ (Tabari, 3/450).

There is another account in Tabari that describes the same events: ‘People surrounded Ali and told him: “We will pledge allegiance to you. Do you not see what they have done to Islam?” Ali (AS) replied:

“Leave me and go to another person for we are moving towards a future uncertain. Time is pregnant with incidents which would terrorize the hearts and paralyze the minds.”
They responded: “By God! Are you not in agreement with us, do you not see the present state of Islam, and the ongoing sedition? Do you not fear God?”

Imam (AS) said:

“I have given you my opinion. So beware! For if I accept the Caliphate, I will act based on my knowledge and learning; and if you leave me now, I would continue my life just like you, and would be obedient to the future Caliph’’ (Tabari, 3/456).
That was Tabari’s description of the event. Imam Ali, however, describes people’s rush to his house in the following manner:

‘They leapt upon me as the camels leap upon each other on their arrival for drinking water, having been let loose after unfastening of their four legs till I thought they would either kill me or kill one another in front of me.’ (Nahjul-Balāgha, Sermon 54).

In another sermon, he relates:

‘At that moment, nothing took me by surprise, but the crowd of people rushing to me. It advanced towards me from every side like the mane of the hyena so much so that Hasan and Hussain were getting crushed and both the ends of my shoulder garment were torn. They collected around me like a herd of sheep and goats.’ (Nahjul-Balagha, Sermon 3)

Investigating the history of the election and the pledge of allegiance makes clear that such a large and harmonious mass movement, which faced such minor opposition at the time, was unprecedented. The opponents and disputants who emerged were those who used to benefit from the previous Caliph, for example, Zayd ibn Thabit, Uthman’s treasurer, to whom Abu Ayyub Al-Ansari said: ‘The reason behind you being against taking the oath of loyalty to Ali is that you were given substantial amounts of gold and silver by the previous Caliph.’

Totally assured and certain, the Imam started a series of fundamental structural reforms in order to eliminate the causes of peoples’ sufferings. Unfortunately, however, according to the Imam himself, there were three groups who did resist against these reformations:

When I took up the reins of government one party broke away and another turned disobedient while the rest began acting wrongfully… Behold! By God who split the grain and created living beings! If people had not come to me and supporters had not exhausted the argument and if there had been no pledge of Allah (SWT) with the learned to the effect that they should not acquiesce in the gluttony of the oppressor and the hunger of the oppressed I would have cast the rope of Caliphate on its own shoulders, and would have given the last one the same treatment as to the first one. Then you would have seen that in my view this world of yours is no better than the sneezing of a goat. (Nahjul-Balagha, Sermon 3)
Source: Shīa Islam: History and Doctrines, Ayatullāh Jaʿfar Subḥānī, Chapter 8