1. The Shi‘ah during the Period of the First Four Caliphs
The Shi‘ah during the reigns of the first three caliphs, viz. Abubakr, Umar and ‘Uthman, has distinctive features which can be expressed in the following manner:
1. During the reigns of these three caliphs, the Shi‘ah were subjected to many pressures with the exception of the initial days after the event of Saqifah. It can even be said that many of the Shi‘ah were deprived of key positions on account of their being Shi‘ah.
2. After the event of Saqifah which brought about dichotomy on the issue of leadership over the Muslims and led to the division of Muslims into two main groups, the Ahl as-Sunnah were referring to the caliphs of the time on the scientific, jurisprudential, ideological, and other problems, whereas the Shi‘ah were referring to ‘Ali (‘a).
The Shi‘ah’s practice of referring to ‘Ali (‘a) regarding scientific issues, jurisprudence and other Islamic sciences in general, continued with the pure Imams (‘a) after the martyrdom of ‘Ali (‘a).
The reason behind the Sunni-Shi‘ah difference in jurisprudence {fiqh}, hadith, tafsir {exegesis of the Qur’an}, kalam {scholastic theology}, among others is this very fact that the reference authorities of these two groups were different and distinct from each other.
3. Just as ‘Ali (‘a) had unofficial political and military cooperation from afar with the caliphs of the time as far as protection of the lofty interests of Islam was concerned, a number of distinguished Shi‘ah among the Companions also assumed military and political positions with the consent of Imam ‘Ali (‘a). For example, Fadhl ibn al-‘Abbas—‘Ali’s (‘a) cousin and defender during the event in Saqifah—held a military position in the army of Sham and passed away in 18 AH in Palestine.
Hudhayfah and Salman became the governors of Mada’in one after the other. ‘Ammar ibn Yasir was appointed by the second caliph as the governor of Kufah after the tenure of Sa‘d ibn Abi Waqqas.
Hashim Mirqal, who was one of the sincere Shi‘ah of the Commander of the Faithful (‘a) and was martyred in the Battle of Siffin on the side of the Imam (‘a), was one of the outstanding commanders during the periods of the three caliphs and conquered Azerbaijan in 22 AH. ‘Uthman ibn Hunayf and Hudhayfah ibn Yaman were commissioned by ‘Umar to measure the lands of Iraq.
‘Abd Allah ibn Badil ibn Waraqa’ al-Khaza‘i, one of the Commander of the Faithful’s (‘a) Shi‘ah whose son was one of the first martyrs in the Battle of Jamal (Camel), was one of the military commanders and conquered Isfahan and Hamedan.
Similarly, individuals such as Jarir ibn ‘Abd Allah Bajalli and Qurzah ibn Ka‘b al-Ansari who were among the Commander of the Faithful’s (‘a) distinguished men during his caliphate, held administrative and military positions during the periods of the three caliphs. Jarir conquered the territory of Kufah and became the governor of Hamedan during ‘Uthman’s reign. Qurzah ibn Ka‘b al-Ansari also conquered Shahr-e Rey during the period of ‘Umar ibn al-Khattab.

Manifestation of Shi‘ism during the Caliphate of ‘Ali (‘a)
Although the root of Shi‘ism can be traced back to the time of the Prophet (S), its manifestation came after ‘Uthman’s assassination and ‘Ali’s (‘a) caliphate. During this period the demarcating line became clear as ‘Ali’s (‘a) supporters and followers openly declared and expressed their Shi‘ism. Shaykh al-Mufid narrates, thus:
A group of people came to ‘Ali (‘a) and said: “O Commander of the Faithful! We are among your Shi‘ah.” The Imam (‘a) looked carefully at their faces and said: “But why can’t I see the countenances of the Shi‘ah in you?” They asked: “O Commander of the Faithful! How should countenances of the Shi‘ah be?”
He (‘a) said: “Their faces are pale from excessive acts of worship at night; their eyes are weak from weeping profusely; their backs have curvature for standing for long time in prayer; their stomachs can reach their backs for fasting a lot; and the dust of humility and lowliness has settled in them.”
Also, poems were recited during the caliphate of Imam ‘Ali (‘a) in which ‘Ali (‘a) has been described as the rightful Imam and successor, and the leader after the Prophet (S). As Qays ibn Sa‘d was saying,

و عليّ إمامنا و إمام لسوانا أتى به التنـزيل

‘Ali is our Imam and that of others. The Qur’an has been revealed for this purpose.
Khuzaymah ibn Thabit Dhu’sh-Shahadatayn used to say:

فديت عليّاً إمام الورى سراج البريّة مأوى التّقى
وصيّ الرّسول و زوج البتول إمام البريّة شمس الضّحى
تصدق خاتمه راكعاً فاحسن بفعل إمام الورى
ففضّله الله ربّ العباد و أنزل في شأنه هل أتى

May I be the ransom of ‘Ali! He is the Imam of the people, the light of creation and the asylum of the God-conscious ones.
He is the successor {wasi} of the Prophet, the husband of Batul (Fatimah), the Imam of creation, and radiant sun.
He is the Imam of creation and gave in alms {sadaqah} his ring while he was in the state of bowing {ruku‘}, and what a good deed he performed!
God, the Exalted, made him superior to others and revealed the Surah “Hal ata” about him.
In some poems, the Imam’s (‘a) Shi‘ah also introduced themselves to the religion of ‘Ali (‘a). For example, while engaged in a fight against a person named ‘Amru ibn Yathribi from among the army of Jamal {camel} during the Battle of Jamal, ‘Ammar ibn Yasir recited thus:

لا تبرح العرصة يا ابن يثربي حتى اقاتلك على دين علي نحن و بيت الله اولى بالنّبي

O Ibn Yathribi! Leave not the battlefront so that we could fight against you over the religion of ‘Ali. I swear to the House of God that we are the foremost ones to the Prophet.
Even the enemies and adversaries were using the same descriptions for the Shi‘ah. For example, in a poem, proud of killing the supporters of ‘Ali (‘a), ‘Amru ibn Yathribi says:

ان تنكروني فانا ابن يثربي قاتل عِلباء و هِند الجملى ثمّ ابن صوحان على دين عليّ

If you do not know me, I am Ibn Yathribi, the killer of ‘Ilba’ and Hind al-Jamali. I am also the killer of Ibn Sawhan for the crime of following the religion of ‘Ali.

2. The Shi‘ah during the Period of the Umayyad Caliphate
The period of the Umayyad caliphate was the most difficult time for the Shi‘ah, starting from 40 AH up to 132 AH. All the Umayyad caliphs with the exception of ‘Umar ibn ‘Abd al-‘Aziz were sworn enemies of the Shi‘ah. Of course, after caliph Hisham the Umayyads were preoccupied with the campaign against internal revolts and the ‘Abbasid movement and the past harsh treatments of Shi‘ah were lessened.
The Umayyad caliphs were living in Sham, the capital of the Umayyad rule, and in most cases, the rulers adopted the policy of bloodshed with respect to the Shi‘ah-populated territories, exerted pressure on the Shi‘ah.
Among all the enemies, it was the Umayyad rulers who focused most on the Shi‘ah relentlessly annoying and disturbing them, with ‘Ubayd Allah ibn Ziyad and Hajjaj ibn Yusuf being most notorious among them.
Ibn Abi’l-Hadid, the well-known scholar in the Sunni world, thus writes: The Shi‘ah were being killed wherever they were. The Umayyads used to mutilate the hands and feet of individuals for being suspected as Shi‘ah. Anyone who was noted for his love and attachment to the family of the Prophet would either be imprisoned, his possessions be plundered, or his house be demolished. The pressure and restrictions imposed upon the Shi‘ah reached a point where the charge of friendship with ‘Ali (‘a) was considered as worse than the accusation of disbelief {kufr} and infidelity, entailing severer punishments.
In adopting this violent policy, living conditions for the people of Kufah was the worst because Kufah was the Shi‘ah capital of the time.
Mu‘awiyah designated Ziyad ibn Sumayyah as the ruler of Kufah and later on assigned the governorship of Basrah to him. Ziyad was once in the rank of the supporters of ‘Ali and he knew them all very well. He pursued the Shi‘ah and found them in whatever nook and corner they would hide. He killed them; threatened them; mutilated their hands and feet; blinded them; hung them on palm trees; and expelled them from Iraq so much so that not a single well-known Shi‘ah remained in Iraq.
Abu’l-Faraj ‘Abd ar-Rahman ibn ‘Ali ibn al-Jawzi has said: When a number of the Shi‘ah protested against Ziyad, who was then delivering sermons from the pulpit, he ordered the mutilation of the hands and feet of eighty persons. He used to gather the people in the mosque and ask them to curse ‘Ali and if anyone refused to do so, Ziyad would order that his house be demolished.
Ziyad, who ruled alternately for six months in Kufah and the next six months in Basrah, appointed Samurah ibn Jundab as his deputy in Basrah so that he could administer the city during his absence. During that period Samurah killed 8,000 people. Ziyad once asked him: “Are you not afraid that you might have killed one innocent person among them?” He replied: “Even if I have to kill two times that figure, I am not afraid of such a thing.”
Abu Suwar ‘Adwi says: “One morning, Samurah {killed} 47 persons from among relatives, all of whom were memorizers of the Qur’an {hufaz}.”
Mu‘awiyah, in a directive to his officials and workers, wrote that they should not accept the testimony of even one of ‘Ali’s (‘a) Shi‘ah or family members. In another directive, he thus wrote: If two individuals would give testimony that a certain person is among the friends of ‘Ali and his family, his name should be erased from the record of the public treasury {bayt al-mal} and his salary and stipend should be cut off.
After subjugating Mecca and Medina,Hajjaj ibn Yusuf, the bloodthirsty and cruel Umayyad agent, was appointed as the governor of Iraq, the center of the Shi‘ah gathering, in 75 AH by the Umayyad caliph ‘Abd al-Malik ibn Marwan. Having covered his head and face, Hajjaj entered the mosque of Kufah incognito. He passed by the line of people and mounted the pulpit.
He remained silent for a long moment. Murmuring among the people started as to who he is. One person said, “He is the new ruler.” The other one said, “Let us pelt him with stone.” Many others said, “No, let us listen to what he will say.” When the crowd silenced, he uncovered his face and uttering a few sentences, he terrified the people so much so that the small stones in the hands of those who were ready to pelt him fell on the ground spontaneously. At the beginning of his speech, he thus said: O people of Kufah! It has been for many years that you have taken chaos, sedition {fitnah} and insubordination as your slogan. I can see heads similar to ripe fruits that must be separated from the body. I shall strike on your heads to such an extent that you would find the way to submission.
Hajjaj implemented a rule of terror throughout Iraq and the eastern districts and unjustly killed many prominent figures of Kufah and pious people.
Mas‘udi thus writes about the crimes of Hajjaj: Hajjaj ruled for twenty years and the number of those who were killed during this period by the swords of his headsmen or torturers exceeded 120,000 people. This figure does not include those who were killed by Hajjaj’s forces in the war against him.
At the time of Hajjaj’s death, 50,000 men and 30,000 women were languishing in his infamous prison. Among them 11,000 were naked. Hajjaj used to imprison men and women in one cell. His prison cells were roofless. As such, the prisoners were not secure from the summer heat or the winter rain and cold.
The Shi‘ah were usually victims of Hajjaj’s prison, torture, persecution, and murder. The best evidence that reflects the miserable plight of the Shi‘ah during the Umayyad period and the intensity of the Umayyad policy of strangulation is the complaint of the Shi‘ah to Imam as-Sajjad (‘a) about the oppression and tyranny perpetrated against them. The late Majlisi has narrates: The Shi‘ah came to Imam Zayn al-‘Abidin (‘a) complaining about the pressure and strangulation, saying: “O son of the Messenger of Allah! We were expelled from our cities and eliminated by atrocious killing. They cursed the Commander of the Faithful (‘a) in the cities as well as in the mosque of the Messenger of Allah (S), on top of his pulpit.
No one prevented it and if any of us would protest, they would say, “This is a turabi (i.e. Shi‘ah); they would report it to the ruler, writing to him that so-and-so has said something good about Abu Turab (Imam ‘Ali (‘a)). The ruler would order them to beat that person, imprison him and finally kill him.”

Summary
After the event of Saqifah, the Shi‘ah would refer to the pure Imams (‘a) with respect to scientific, jurisprudential and ideological issues. Although they were cooperating with the caliphs of the time in line with the interests of Islam, most of them were deprived of administrative positions.
During the caliphate of the Commander of the Faithful (‘a), expression of Shi‘ism was one of the distinctive features of the Shi‘ah.
The period of the Umayyad rule was one of the most difficult times for the Shi‘ah. All the caliphs, with the exception of ‘Umar ibn ‘Abd al-‘Aziz, were sworn enemies of the Shi‘ah, and the Shi‘ah-populated regions the bloodthirsty and cruel governors were ruling over.