In spite of severe strangulation and oppression perpetrated against the Shi‘ah during the Umayyad rule, the spread of Shi‘ism continued unabated. The reason behind this was the state of oppression of the family of the Prophet (S) which prompted the people to incline emotionally toward them, causing new individuals to continuously embrace the creed of Shi‘ism.
This point was completely conspicuous during the end of the Umayyad rule. The spread of Shi‘ism during the Umayyad rule had several stages, each of which had its own salient features. The overall stages can be divided as follows:
a) From 40 AH to 61 AH (the period of Imam al-Hasan and Imam al-Husayn (‘a));
b) From 61 AH to approximately 110 AH (the period of Imam as-Sajjad and Imam al-Baqir (‘a)); and
c) From 110 AH to 132 AH, i.e. till the end of the Umayyad rule (the period of Imam as-Sadiq (‘a).

a) The Period of Imam al-Hasan and Imam al-Husayn (‘a)
From the time of the Commander of the Faithful (‘a), the Shi‘ah was gradually formed into a distinct group and the line of the Shi‘ah was obviously clear.
For this reason, in the peace treaty with Mu‘awiyah, Imam al-Hasan (‘a) stipulated the guarantee of the Shi‘ah of his father’s safety as one of the articles of the peace treaty, and nobody should protest against them. The Shi‘ah gradually trained themselves to accept that obedience to the Imam does not depend on the Imam’s actual grip on power. As such, when the people were pledging allegiance to Imam al-Hasan (‘a), he made it a condition for them to obey him both in war and in peace.
In the same manner, it was made clear that Imamate {imamah} is not necessarily equal to governance and that a tyrant ruler such as Mu‘awiyah cannot be the Imam, obedience to whom is obligatory. For example, in the sermon that he delivered in the mosque of Kufah after the peace treaty at the insistence and in the presence of Mu‘awiyah, Imam al-Hasan (‘a) said: The caliph is he who practices the Book of Allah and the Sunnah of the Prophet (S), and he who is practicing injustice cannot be the caliph. He is rather a king who controls a kingdom. He shall enjoy for a short period and after that, his joy shall be curtailed and he must be called to account.
Among the salient features of the Shi‘ah’s society at this stage is the unity and solidarity among them, which resulted from the status of the Shi‘ah leaders. Until Imam al-Husayn’s (‘a) martyrdom, we cannot see of any split among the Shi‘ah. Imams al-Hasan and al-Husayn (‘a) had a certain status in the sight of Muslims which none of the pure Imams (‘a) after them ever attained.
They were the well-established progeny of the Prophet (S). During the Battle of Siffin, when he saw that Imam al-Hasan (‘a) was enthusistically rushing toward the battlefront, the Commander of the Faithful (‘a) said: “Hold back this young man on my behalf, lest he causes my ruin, because I am unwilling to send these two (al-Hasan and al-Husayn) toward death, lest the descending line of the Prophet (S) is cut away by their death.”
Imams al-Hasan and al-Husayn (‘a) also occupied a position of respect among the Companions of the Prophet (S). This fact was demonstrated in the people’s pledge of allegiance to Imam al-Hasan (‘a) in which the Companions of the Prophet (S) accepted his caliphate and none protested. As such, during Imam al-Hasan’s (‘a) caliphate we cannot see any problem (in terms of his legitimacy being challenged) except from Sham.
When the Imam (‘a) concluded a peace treaty and wanted to leave Kufah to return to Medina, the people wept profusely. In Medina also, his position is clear from a Qurayshi’s report to Mu‘awiyah. In his report to Mu‘awiyah, a Qurayshi man thus wrote: O Commander of the Faithful! Hasan performs his dawn prayer in the mosque and he remains in the state of prostration till the sun rises. Then, he inclines to one of the mosque’s pillars and anyone who is in the mosque can benefit from his services and talks to him until the rising of the sun {at noon}. He performs a two-rak‘ah prayer, stands up, goes out, asks about the condition of the wives of the Prophet (S), and then returns to his house.
Imam al-Husayn (‘a), like his distinguished brother, occupied a highly respectable position such that even ‘Abd Allah ibn Zubayr, a staunch enemy of the Ahl al-Bayt (‘a), could not deny the station of Imam Husayn (‘a). While the Imam (‘a) was still in Mecca, the people were not paying attention to Zubayr halting the progress of his campaign. Thus, he wanted the Imam (‘a) to leave Mecca as soon as possible. He said to Imam al-Husayn (‘a), hence: “If I had the same position you have in Iraq, I would have hastened to go there.”
The station of the Imam (‘a) was such that his refusal to pay allegiance to the caliph rendered the government of Yazid to be questioned. It was for this reason that the ruling authority insisted on him giving his pledge.
These two persons were held in such high esteem and respect among the Banu Hashim that not only could none from Banu Hashim have a leadership claim during their lifetime, but also none could even claim to be the chief of the Banu Hashim. When Imam al-Hasan (‘a) passed away on the account of the effect of poison given by Mu‘awiyah, ‘Abd Allah ibn al-‘Abbas was then in Sham. Mu‘awiyah said to him: “Ibn al-‘Abbas, Hasan died and you became the chief of the Banu Hashim.” Ibn al-‘Abbas said: “So long as Husayn is there, I am not.”
Even Ibn al-‘Abbas, in spite of his intellectual and political position, being a reporter of hadith and exegete of the Qur’an and, according to the Sunnis, even higher in rank than Imams al-Hasan and al-Husayn (‘a), was offering services to them. It is thus narrated in the document of Ibn Abi Ziyad: Ibn al-‘Abbas prepared the riding horses of Hasan and Husayn, keeping the stirrup until they rode. I said: “Why are you keeping stirrup for them even though you are older than them?” He said: “You fool! Don’t you know who they are? They are the sons of the Messenger of Allah. Is it not a great honor that God has granted me the opportunity to keep the stirrup for them?”

The Impact of the Karbala’ Movement on the Spread of Shi‘ism
After Imam al-Husayn’s (‘a) martyrdom the Shi‘ah, owing to the loss of one of their key supporters, were extremely frightened losing hope in an armed confrontation with the enemy. With the occurrence of the heart-rending event of ‘Ashura’ the Shi‘ah movement received a devastating blow within a very short period of time.
As the news of this event spread within the Muslim lands, especially in Iraq and Hijaz, intense fear prevailed in the Shi‘ah communities. This was because it became increasingly clear that Yazid is determined to stabilize his rule even to the extent of killing the son of the Prophet (S), taking as captives his women and children, and that he would not refrain from any crime in order to strengthen the pillars of his government.
The effect of this intense apprehension was most obvious in Kufah and Medina, and it multiplied with the Hirrah tragedy and the intense and merciless crackdown of the popular ‘Medina movement’ by Yazid’s forces. Severe strangulation in the Shi‘ah-populated territories of Iraq and Hijaz especially in Kufah and Medina, was rampant shattering the Shi‘ah cohesion and formation.
In describing this sorrowful condition, Imam as-Sadiq (‘a) says: “After the martyrdom of Imam al-Husayn (‘a), the people dispersed from around the family of the Prophet (S) except three persons, viz. Abu Khalid Kabuli, Yahya ibn Umm at-Tawil and Jabir ibn Mut‘am.”
In describing this period, Mas‘udi the historian also says: “‘Ali ibn al-Husayn assumed the Imamate secretly with utmost dissimulation {taqiyyah} at a difficult time.”
This state of affairs persisted till the end of Yazid’s rule. After Yazid’s death, the Shi‘ah movements started and continued till the stabilization of the Umayyad rule during the caliphate of ‘Abd al-Malik. This period was a good opportunity for the spread of Shi‘ism.
One of the important impacts of the Karbala’ movement was the delegitimization of the Umayyad rule in the public opinion. The infamy of the government reached a point where the position of caliphate was in its lowest degree and the people were no longer viewing it as a sacred institution.
The poem below addressed to Yazid’s grave in Hawarin expresses this infamy:

أيّها القبر بحوارينا قد ضمنت شر النّاس أجمعينا

O grave that is in the city of Hawarin! The worst of people is inside you.
At that time, with the exception of the people of Sham, the Muslims - both Sunnis and Shi‘ah - were opposing the Umayyad caliphate and Sunni and Shi‘ah revolts were frequently happening. Ya‘qubi thus writes:
‘Abd al-Malik ibn Marwan wrote to his governor Hajjaj ibn Yusuf: “Do not afflict us with the shedding of the blood of the progeny of Al Abi Talib because we saw what fate the Sufyanis (descendants of Abu Sufyan) met as the result of their killing.”
Finally, the blood of Imam al-Husayn (‘a) demolished the palace of the Umayyads. Muqaddasi says: “As God saw the oppression and injustice of the Umayyads against the family of the Prophet (S), He gathered an army from the different parts of that Khurasan and sent it to them at the darkness of the night.”
Meanwhile, the state of oppression of Imam al-Husayn (‘a) and the martyrs in Karbala’ expressed the love for the progeny of the Prophet (S) in the hearts of the people and strengthened their position as the descendants of the Prophet (S) and the true protectors of Islam.
Most of the uprisings during the Umayyad period took place in the name and for the sake of avenging their blood, and revolutions used to be formed under the slogan, “Ya litharat al-Husayn” {O helpers of Husayn!}. Even the uprising of a person like Ibn Ash‘ath in Sistan was formed under the name of Hasan al-Muthanna (son of Imam al-Hasan (‘a)).
For this reason, the hadiths regarding Imam al-Mahdi (‘a) as the avenger {muntaqam} of the progeny of Muhammad (S) gained prominence. The people were waiting for the avengers against the Umayyads and due to impatience and the peak of waiting, they would sometimes conform the name “Mahdi” to the name of leaders of the movements and uprisings.
In the meantime, the pure Imams (‘a) and the progeny of the Prophet (S) kept on reviving the memory and reminiscence of the martyrs of Karbala’. Whenever he desired to drink water, Imam as-Sajjad (‘a) would shed tears profusely when he set his sight on the water. When he was asked about the reason behind this reaction, he (‘a) said: “How could I not cry when the water was set free for the wild animals and beasts of prey of the deserts, but it was denied to my father?” One day, a servant of the Imam (‘a) said: “Is there no end for your agony?”
The Imam (‘a) said: “Woe unto you! Ya‘qub, who on account of the disappearance of only one of his twelve sons, so cried a lot during their separation that his eyes turned blind and on account of his agony his back bent. This is while his son was alive. But I was an eyewitness to the killing of my father, brothers, uncles and 18 persons from among my relatives whose corpses were scattered on the ground. So, how could it be possible for my agony and anguish to end?”
Imam as-Sadiq (‘a) was encouraging the poets to recite poetry as elegy to Imam al-Husayn (‘a), saying: “Whoever would keep on reciting poem about al-Husayn (‘a) and prompt the people to cry, paradise shall be incumbent upon him and his sins shall be forgiven.”
In this way, Imam al-Husayn (‘a) became the symbol of Shi‘ism. As such, in many stages of history such as the period of caliph Mutawakkil visitation {ziyarah} to the grave of the Imam (‘a) was forbidden.

Summary
From the time of the Commander of the Faithful (‘a), the Shi‘ah gradually formed into a particular group and party, and the rank of the Shi‘ah became completely distinct. Meanwhile, on account of the station of Imams al-Hasan and al-Husayn (‘a), the Shi‘ah of the time enjoyed unity and solidarity and no split was yet observed.
After the martyrdom of Imam al-Husayn (‘a), the Shi‘ah lost their key support and experienced intense fear and apprehension. Only a small number remained beside Imam as-Sajjad, but after the death of Yazid, this state of affairs changed. The movement of Karbala’ removed the legitimacy of the Umayyad rule and dragged the position of caliphate from its sanctity to its lowest ebb. In the meantime, the love for the progeny of the progeny of the Prophet (S) was manifested in the hearts of the people.