The revolt against Uthman and his assassination...
The revolt against Uthman and his assassination, the outbreak of armed conflicts between the constituted authority of Imam Ali (a.s.) and the seccesionist Mu'awiyya bin Abi Sufyan are all proofs of political differences. As a result, two governments existed in the Islamic community, the cause of which was political differences, as well as, the differences in understanding and applying of the Book and the Sunna.
One of these two governments represented the Omayyads, which was considered, by the companions, as having submitt-ed to Islam by force (after oppressing and subsequently fighting it). The second government consisted of Imam Ali (a.s.) and the Prophet's companions `sahaba' both the immegrants `Muhajirin' and the helpers `Ansar' who made up the vanguards for building Islam under the leadership of Imam Ali (a.s.), and saw his superiority in the field of leadership and legislation.
When the two governments became distinct from one another, the Omayyad government consolidated its power by adopting the ideological conflicts and tyrannizing the scholars and men of political and jurisprudential thought who subscribed to the school of Ali and his household `Ahlul-Bait' . This action was meant to exclude them from the political struggle thereby eliminating any political opposition.
A war of propaganda and slander was waged against the followers of Ah-lul-Bait (a.s.) and their ideology. Then came the Abbasids dynasty which proved more oppressive and terroristic to the Ahl-ul-Bait (household) of the Holy Prophet (a.s.). It is noteworthy that the tyranny of these dynasties did not stop at the Imams of the Ahl-ul-Bait (a.s.), and the scholars of their school, but affected the founders of other Islamic schools, as well.
Those people with political interests, the sycophants and beneficiaries had their day, sowing those differences between the Muslims, applying it in order to conselidate their power and posing as defenders of this school or that, to gain followers and protectors. Islamic history is replete with bloody wars between the rulers who exploited that destructive weapon.
4- Historical Differences: History is nothing but a register of events and occurances which took place in the past according to the social laws. The Muslims paid great attention in writing the life history of the Prophet (s.a.w.) and Islamic history throughout the ages.