After Ali's death, Kufi Muslims pledged allegiance to his eldest son Hasan without dispute, as Ali on many occasions had declared that just People of the House of Muhammad were entitled to rule the Muslim community.

At this time, Muawiyah held both the Levant and Egypt and, as commander of the largest force in the Muslim Empire, had declared himself caliph and marched his army into Iraq, the seat of Hasan's caliphate.

War ensued during which Muawiyah gradually subverted the generals and commanders of Hasan's army with large sums of money and deceptive promises until the army rebelled against him.
Finally, Hasan was forced to make peace and yield the caliphate to Muawiyah.
Muawiyah then transformed tuned the caliphate into a secular kingdom (Sultanate).
The Umayyad caliphate later became a centralised monarchy under Abd al-Malik ibn Marwan.

Umayyads placed extreme pressure upon Ali's family and his Shia.
Regular public cursing of Imam Ali in the congregational prayers remained a vital institution until Umar ibn Abd al-Aziz abolished the practice, 60 years later.

Madelung writes:
Umayyad highhandedness, misrule and repression were gradually to turn the minority of Ali's admirers into a majority.
In the memory of later generations Ali became the ideal Commander of the Faithful.
In face of the fake Umayyad claim to legitimate sovereignty in Islam as God's Vice-regents on earth, and in view of Umayyad treachery, arbitrary and divisive government, and vindictive retribution, they came to appreciate his [Ali's] honesty, his unbending devotion to the reign of Islam, his deep personal loyalties, his equal treatment of all his supporters, and his generosity in forgiving his defeated enemies.

Ibn Abi'l-Hadid narrates the following about the Umayyad treatment of Ali and his followers:
"Everybody knows that when the Umayyads held the reins of the Islamic world, they spared no single effort for extinguishing the light of Ali and inventing flaws against him.
Moreover, they issued the decisions of cursing him openly from the mimbars of their mosques and sentenced to death anyone who would mention any of his incalculable merits.
They also prevented people from reporting any narration that might refer to any of his accolades.
Finally, they even prevented people from calling their newborns by his name."
After Ali's death, Kufi Muslims pledged allegiance to his eldest son Hasan without dispute, as Ali on many occasions had declared that just People of the House of Muhammad were entitled to rule the Muslim community.
At this time, Muawiyah held both the Levant and Egypt and, as commander of the largest force in the Muslim Empire, had declared himself caliph and marched his army into Iraq, the seat of Hasan's caliphate.
War ensued during which Muawiyah gradually subverted the generals and commanders of Hasan's army with large sums of money and deceptive promises until the army rebelled against him. Finally, Hasan was forced to make peace and yield the caliphate to Muawiyah. Muawiyah then transformed tuned the caliphate into a secular kingdom (Sultanate). The Umayyad caliphate later became a centralised monarchy under Abd al-Malik ibn Marwan.
Umayyads placed extreme pressure upon Ali's family and his Shia. Regular public cursing of Imam Ali in the congregational prayers remained a vital institution until Umar ibn Abd al-Aziz abolished the practice, 60 years later.
Madelung writes:
Umayyad highhandedness, misrule and repression were gradually to turn the minority of Ali's admirers into a majority. In the memory of later generations Ali became the ideal Commander of the Faithful. In face of the fake Umayyad claim to legitimate sovereignty in Islam as God's Vice-regents on earth, and in view of Umayyad treachery, arbitrary and divisive government, and vindictive retribution, they came to appreciate his [Ali's] honesty, his unbending devotion to the reign of Islam, his deep personal loyalties, his equal treatment of all his supporters, and his generosity in forgiving his defeated enemies.
Ibn Abi'l-Hadid narrates the following about the Umayyad treatment of Ali and his followers:
"Everybody knows that when the Umayyads held the reins of the Islamic world, they spared no single effort for extinguishing the light of Ali and inventing flaws against him. Moreover, they issued the decisions of cursing him openly from the mimbars of their mosques and sentenced to death anyone who would mention any of his incalculable merits. They also prevented people from reporting any narration that might refer to any of his accolades. Finally, they even prevented people from calling their newborns by his name."
Ali