There was no Difference in the Policies of Imam Hassan (A.S) and Imam Husayn A.S: However, close investigation proves the contrary, as we see that al-`Imam al-Hasan (AS) lived for about nine and a half years during the reign of Mu`awiyah and did not oppose him overtly. After the martyrdom of his brother, al-`Imam al-Husayn (AS) also lived for about nine and a half years during the reign of Mu`awiyah and never thought of rising in rebellion against him and did not challenge him.

Hence, the main cause of this superficial difference in the policies of the two Imams (AS) lies in the difference of opinion between Mu`awiyah and Yazid, rather than the difference of opinion of these two great Imams (AS).
The policy of Mu`awiyah was not based on lack of discipline and restraint and he did not deride the religious precepts by its overt opposition.
Mu`awiyah called himself a “companion” of the Holy Prophet (SA) and the “writer of Revelation”. Through his sister (who was the wife of the Holy Prophet (SA) and who was Umm al-Mu`minin (the mother of the believers), Mu`awivah was called “Khal al-Mu`minin” (the maternal uncle of the believers) and was greatly favoured by the Second Caliph in whom the common people had total confidence and special attachment.
Furthermore, Mu`awiyah, in a majority of cases, had appointed the Companions of the Holy Prophet (SA) who were respected and honoured by the people (such as Abu Hurayrah,` Amr al-`As, Samrah, Yusr, Al-Mughirah ibn Shu`bah, and others) as governors of provinces and had put them in charge of the key positions of the country. These governors used to work for the favourable opinions of the people towards Mu`awiyah. Many ahadith were fabricated and narrated among the people regarding the virtues and the religious immunity of the Companions of the Holy Prophet (SA) and that they were not questionable for whatever they did. Thus whatever Mu`awiyah did, if corrigible and justifiable at all, it was rectified and justified by these authorities; otherwise, by giving a great deal of hush-money, he prevented his opponents from complaining. Where these means and methods did not work, thousands of innocent people comprising of Shi`ahs (friends) of `Ali (AS), other Muslims, and even a great number of the Companions of the Holy Prophet (SA) were killed by these collaborators, partisans, and “companions” of Mu`awiyah.
Mu`awiyah pretended to be right in whatever he did and accomplished everything with a special patience and forbearance. With a particular gentleness and flexibility, he attracted the kindness and obedience of people. Sometimes, he even heard the curse of people on him and sensed their enmity, but he responded with cheerfulness and forgiveness and thus pursued his policy in this way.
Apparently, he paid respect to al-`Imam al-Hasan (AS) and al-`Imam al-Husayn (AS) and sent them valuable gifts and souvenirs. On the other hand, he publicly announced that whoever narrates a hadith concerning the virtues of the Ahl al-Bayt (AS),will have no security of life, reputation, and property; but whoever narrates a hadith concerning the virtues. Prophet (SA) will receive a of the Companions of the Holy reward.
He gave orders to the orators and preachers to curse al-`Imam `Ali (AS) from pulpits used for addressing Muslims. By the order of Mu`awiyah, his hirelings killed the supporters of al-`Imam `Ali (AS) wherever they could find them. They went along in this matter to such an extent that they killed a large number of people who were the enemies of al-`Imam `Ali (AS), accusing them of having friendship with the Imam (AS).
It becomes clear from the above description that the rise of al-`Imam al-Hasan (AS) would only have ended to the detriment of Islam and would have had no effect other than the martyrdom of the Imam (AS) and his supporters. And even it was not unlikely that, in this case, Mu`awiyah might have got killed al-`Imam al-Hasan (AS) through the friends and relatives of the Imam (AS) and then, in order to pacify public opinion, Mu`awivah would have rent (torn) his shirt and mourned for the Imam (AS) and, in seeking vengeance (for this bloodshed), he would have tried to take his revenge by killing the Shi`ahs, as he later did while dealing with the case of `Uthman.
But the political trend of Yazid had no resemblance with that of his father. He was a self-admiring and indisciplined youth. He had no logic: other than force. He gave no importance to public opinion.
During his short-term rule, Yazid at once revealed the damages which were secretly inflicted on Islam.
In the first year of his rule, Yazid put the family of the Holy Prophet (SA) to the edge of the sword.
In the second year of his rule, he ruined the city of Madinah and allowed his troops to transgress upon the honour, life, and property of the people for three days.
In the third year of his rule, he destroyed Ka`bah.
Owing to the above reasons, the movement of al-`Imam al-Husayn (AS) was imprinted on the minds of the people and its effect grew more profoundly and publicly day by day. In the beginning, this movement manifested itself in the form of bloody revolutions. Finally, it attracted a great number of Muslims as the supporters of truth and reality and as the supporters of the Ahl al-Bayt (AS) of the Holy Prophet (SA).
It was because of this reason that Mu`awiyah, in his will to Yazid, had strongly recommended that Yazid should leave al-`Imam al-Husayn (AS) alone and not bother him; but would the drunkenness and self-admiration of Yazid permit him to differentiate between his benefit and his loss?