It is correct as you say that in pre-Islamic days we were united and at peace with each other. But have you realized that dissensions and disunity between us started with the dawn of Islam. The reason was that we accepted and preached Islam and you remained heathen. The condition now is that we are faithful and staunch followers of Islam and you have revolted against it. Even your original acceptance was not sincere, it was simple hypocrisy. When you saw that all the big people of Arabia had embraced Islam and had gathered under the banner of the Holy Prophet (s) you also walked in (after the Fall of Makkah.)
In your letter you have falsely accused me of killing Talha and Zubayr, driving Ummul Mu'minin Aisha from her home at Madina and choosing Kufa and Basra as my residence. Even if all that you say against me is correct you have nothing to do with them, you are not harmed by these incidents and I have not to apologize to you for any of them.
You have threatened that you are coming out to fight against me with a large horde of Muhajirs and Ansar. Do tell me who these Muhajirs are? The door of Hegira (Migration of Muslims to save their lives from the hands of unbelievers of Quraysh) was already closed on the day your elder brother, Yazid bin Abi Sufyan was taken prisoner and Makkah was surrendered by your father and the process of migration had ceased as soon as your paganism ceased. (The Holy Prophet (s) had said that there would be no Hegira after the victory of Makkah).
Are you so anxious for a battle? Wait! You may get it to your heart's content. I may come out myself to meet you which will be a correct gesture on my part because Allah may have destined me to punish you for your inequities. And if you take the initiative to come out to fight, then it would mean, as a poet of Bani Asad has said "They are facing those furious summer winds which shower sand, rubble and gravel-stones". Remember that I still hold the sword which has sent your maternal grandfather, maternal uncle and your brother to the same resting-place, the Hell.
By Allah, I know you too well to argue with you or to advise you. Apostasy and avariciousness have taken a firm hold of your mind, your intelligence is of inferior order and you cannot differentiate what in the end is good for you and what is not.
It is correct to say about you that you have risen to such dangerous and sinful heights that your fall which is inevitable will lead to an eternal damnation because you are coveting a thing which morally does not belong to you and for which you are religiously most unsuitable and with which you have neither sincere affection nor any affinity or propensity. It had been once usurped from the right person and you now want to retain it for yourself.
How great is the difference between your words and deeds? How much you resemble your maternal and paternal uncles, whose ill-luck persuaded them to deny and repudiate the Holy Prophet (s) and to fight against him and everyone of whom was at last doomed to die. You know very well that they could not protect themselves or protect the cause they were challenging to men who were energetic and brave and were present in every battlefield to defend the cause of Islam.
You have also written so much about the murderers of Caliph Uthman. The correct thing for you to do is to take the oath of allegiance to me as others have done and present the case in my court of justice and then I shall pass my judgement according to the tenets of the Holy Qur'an. But what you are desiring now is a deceit usually played upon babies when they are to be checked from breast feeding.
May the Peace of Allah be upon those who deserve it.