Those who first embraced Islam were the people whose hearts were freed from the remains of the vicious pre-Islamic traditions and vile fanaticism. Their souls were open to what the Prophet of Allah called them to believe in. They were people of justice, moderation and faith - indeed the saved ones. But there were others whose interests were to cause chaos and divide the unity of the nation, the kind of people who neither embraced Islam nor rid their souls of their destructive doctrines and poisonous ideas. They hid under the name of Islam and kept spreading evil and dividing the nation. Some of them embraced the ideas of Mazdaism or the principles of paganism while alleging they were Muslims and those they were preaching Islam, bringing the number of deviated groups that preach Islam to more than seventy.
Muslims after the death of the Prophet were on the same standing with regard to all the details of Islam, except of course those who showed unity and concealed hypocrisy. Thereafter came the dissension of the apostates and Musaylama the Liar, then the battles with the dissidents who declared disobedience at the time of Caliph Ali bin Abi Talib (may Allah be satisfied with him).
As it is quite known, disobedience must not be declared against the ruler unless he shows blatant infidelity as in the Hadith related by Muslim: “He who disapproves of anything done by his ruler must resort to patience with him, as anyone who dissents against his rule, even in the slightest manner, and die on this condition, would be like he died in the pre-Islamic era before embracing Islam”; and the other well-known, authenticated Hadith related by AI Bukhari and Muslim: “You shall not dispute the ruling of your rulers unless you see from them blatant infidelity” and “blatant” here means beyond confusion. Also there was the dissension of the Khawarij who accused Caliph Ali, Mu’aweya, and the arbiters Abu Moussa AI Ash’ary and Amr bin AI Aass of infidelity for the arbitration. They also accused the followers of AI Jamal, Talha, AI Zubair, Ayisha, and all those who consented the arbitration, of infidelity.
They considered infidel any Muslim who commits a sin, whether small or grave, in contradiction with the consensus of the people of good judgment who saw that no Muslim could be accused of infidelity because of committing a sin unless he considers it lawful for him to practice. The fatalist Mu’tazila followed that group claiming that there were two Creators of people’s doings.
The nation split, but widespread knowledge was there to teach people that the reasons behind the doings of the rulers was not the war against Islam, but to cast away any dissension and only suppress the wicked. We can see that the extremists remained a minority with no influence against the majority of people with the true belief.
But when knowledge decline, and many scholars abandoned their role, and rulers refrained from dealing with abnormalities under different pretexts and various excuses, the dissension grew stronger and the people split into warring groups and sects, bringing the nation to a disgraceful state of weakness and causing it to fall as a result of the successive blows by tendencies emanating from the extended arm of extremist thoughts. That was the big fall.