Schools of Islamic thought (madhahib) are the paths people follow to the Noble Quran and Prophet Muhammad. Obviously, these schools of thought were founded considerably after the death of the Prophet; in fact, they never took shape until the time of the Umayyid Caliphate. The common phrase ahl al-sunnah wal-jama΄ah, for example, became prevalent during the third century of the Hijrah. By the year 250H, the four Sunni schools of thought were being popularized and patronized during the Abbasid Caliphate. The Shi'a school of thought on the other hand, continued its growth and progress after Imam Ali through his descendants who were connected to each other through a chain of narration and knowledge. Prophet Muhammad and the designated imams in the Shi'a school of thought were shielded by Allah from any sin, religious error, or forgetfulness.
Today, the five schools of Islamic thought accepted by all Muslims are the Ja'fari, comprising 23% of the Muslims; the Hanafi, comprising 31% of the Muslims; the Maliki, comprising 25% of the Muslims; the Shafi΄i, comprising 16% of the Muslims; and the Hanbali, comprising 4% of the Muslims. The remaining small percentage follow other minority schools, such as the Zaydi and the Isma΄ili.
The Ja'fari school of thought was headed by Imam Ja'far ibn Muhammad al-Sadiq who lived from 83H to 148H. He was born in and died in the holy city of Madina, and he is the sixth Imam of the twelve designated imams of the school of Ahlul Bayt. Although the fiqh (Islamic Jurisprudence) was developed by the Prophet Muhammad and his successors (i.e., the imams), the fiqh, as taught by the Shi'a, did not have the opportunity to be presented to the masses of people because of the political predicament that the Ahlul Bayt suffered under the rulers for many centuries. The imams refused to acknowledge the legitimacy of the Umayyad and Abbasid caliphs, and their governments; and thus they and their followers were exposed to tremendous harassment and persecution at the hands of the unjust caliphs. Once the Umayyad government became weak, Imam Ja'far ibn Muhammad al-Sadiq found a golden opportunity to formulate and spread the tradition of the Prophet Muhammad and his family. At one time, four thousand scholars, commentators of the Quran, historians, and philosophers attended his classes in the holy city of Madina. Therefore, he was able to pass down the authentic teachings of the Noble Quran and the Prophet Muhammad and crystallize them in what came to be known as al-Fiqh al-Ja'fari, the Ja'fari Jurisprudence. His teachings were collected in 400 usul (foundations) which were written by his students and encompass hadith, Islamic philosophy, theology, commentary of the Quran, literature, and ethics.
After a period of time, three distinguished scholars categorized these 400 usul in four books which are the main sources of hadith for the Shi'a school of thought. They are: Usul al-Kafi by al-Kulayni (d.329H), Man La Yahduruh al-Faqih by al-Saduq (d.381H), and al-Tahdib and al-Istibsar by al-Tusi (d.460H). These three scholars were known as the “three Muhammads” since their first names were all Muhammad. While these four books are the main sources of hadith for the Shi'a, their authors still did not label their books as ”sahih” (authentic). Although they did their best to gather only authentic traditions, but if a particular tradition contradicted the Noble Quran then it was not accepted as legal and valid. Hadith, according to the Ja'fari school of thought, are accepted only if the Noble Quran verifies them, since the Noble Quran is the only undoubtable source of guidance.
The Hanafi school of thought was headed by Imam al-Nu΄man ibn Thabit (Abu Hanifa) who lived from 80H to 150H. Imam Abu Hanifa was born to a non-Arab father, was raised in Kufa, and died in Baghdad. This school of thought prevailed during the time of the Abbasid Empire when a student of Imam Abu Hanifa, Abu Yusuf al-Qadi became the head of the judiciary department and the highest judge, and thus he spread this madhhab (school of thought), in particular, during the caliphates of al-Mahdi, al-Hadi, and al-Rashid. No other man was as close to the Abbasid caliph, Harun al-Rashid as was Abu Yusuf al-Qadi, but the Abbasid caliph, al-Mansur also worked hard to support and consolidate Imam Abu Hanifa's school of thought and to spread his madhhab in the face of the growing popularity of Imam Ja'far al-Sadiq. Imam Abu Hanifa studied under the instruction of Imam Ja'far al-Sadiq for two years, and said in regards to him, “I have not seen anyone more knowledgeable than Ja'far ibn Muhammad, and indeed, he is the most knowledgeable one in the nation.”
The Maliki school of thought was headed by Imam Malik ibn Anas al-Asbahi who lived from 93H to 179H. He was born in the holy city of Madina, and his fame spread throughout Hijaz. On the account of his disagreement with Imam Abu Hanifa, Imam Malik became the leader of the school of tradition (hadith), while Imam Abu Hanifa was the leader of the school of opinion (ra΄i). Yet, most Muslim governments were supportive of Imam Abu Hanifa.
Imam Malik joined the 'Alawiyiin, the descendants of Imam Ali, and received his knowledge from Imam Ja'far al-Sadiq, but thereafter, inconsistencies marked his life. At one point he was oppressed and having earned the anger of the government, he was dragged through the streets by his clothes and lashed. In 148H, his fortunes reversed and he regained his popularity and dominance. The Abbasids tried to set him up as a popular reference for the nation in giving verdicts and injunctions. The Abbasid caliph al-Mansur asked him to write al-Muwatta', his book of fiqh, which contains the principles of the Maliki school of thought. Furthermore, during the hajj season, the official announcer of the government proclaimed that no one had the authority to give fatawas (religious decisions) except for Imam Malik. The Abbasid caliph Harun al-Rashid sat on the floor to listen to him, and the caliphate in general exalted him to the point where they said that no book on earth, except the Noble Quran, was more authentic than that of Imam Malik's. Ibn Hazm al-Andalusi says that two schools of thought were spread due to the government and the sultan: the school of Imam Abu Hanifa, since Abu Yusuf al-Qadi only appointed Hanafi judges; and the school of Imam Malik ibn Anas, for a student of Imam Malik, Yahya ibn Yahya was so respected in the caliph's palace that no judge was ever appointed in Andalus, Spain without his consultation and advice.
The Shafi΄i school of thought was headed by Imam Muhammad ibn Idris al-Shafi΄i who lived from 150H to 198H. Imam Shafi΄i was born in Hijaz and his school of thought emerged in Egypt. At the time of the Fatimid Dynasty, the Egyptians were mainly followers of Ahlul Bayt, and the teachings of Ahlul Bayt were being taught in al-Azhar University. At a later time, Salah al-Din al-Ayyubi came and waged an extensive war against the school of Ahlul Bayt by banning the teaching of their madhhab (school of thought) in al-Azhar and resurrecting the other madhahib, including that of Imam Shafi΄i, who was killed in Egypt in 198H.
The Hanbali school of thought was headed by Imam Ahmad ibn Hanbal who lived from 164H to 241H. He was born and died in Baghdad. He only gained popularity in Najd (a region of the Arabian Peninsula) due to the ideas of Muhammad ibn 'Abd al-Wahhab, the founder of Wahabism. The Hanbali madhhab spread in Najd primarily due to the teachings of Ahmad ibn 'Abd al-Halim al-Dimishqi ibn Taymiyyah (661H-728H) and his student ibn al-Qayyim al-Jawziyya.
A close study of the history of the madhahibs and a search into the reasons for their birth, existence, and spread, reveals that the various governments were the main factor in the birth and spread of these schools. Governmental aid took physical and financial forms by establishing schools, sponsoring books of fiqh (law), adopting and sponsoring official madhahib, and giving freedom to the founders and scholars of some of the “official” madhahib. This trend has occurred in almost every religion worldwide; for example, one might compare this trend in Islam to the birth of the Anglican Church in 1534AD by the English king, Henry VIII who made it the official religious tradition of the state, thus giving it 55 million followers.
History tells that the school of Ahlul Bayt suffered extreme oppression, tyranny, and discrimination at the hands of the Umayyad and 'Abbasid caliphs. But in spite of oppression, by the divine will of Allah, the school of the Ahlul Bayt reached a climax during the caliphate of al-Ma'mun, and Shi'ism reached so far into the governmental dignitaries that al-Ma'mun himself was forced to show deep sympathy towards the 'Alawiyiin, the descendants of Imam Ali, and to show an inclination towards Shi'ism, to the point that he invited Imam Ali ibn Musa al-Rida, the eighth Imam of the Ahlul Bayt to be his successor—a position which Imam al-Rida declined.
 “Bulletin of Affiliation” Al-Madhhab Schools of Thought Statistic - Dec. 1998, Vol. 17-4. 5
 Kalili, Min Amali al-Imam al-Sadiq, Vol. 4, 157
 Tadhkirat al-Hiffadh, Vol. 1, 166; Asna al-Matalib, 55