That is because the people had broken their pledge of...

That is because the people had broken their pledge of allegiance to al-Husayn before he declared war mobilization. Thus his little army was empty of any traitorous person on the day when he stood to fight against his enemies to achieve his ideal objectives. However, the treason from which al-Hasan, peace be on him, suffered at the Camp of Maskan and the Camp of al-Mada'in was quite different from that which al-Husayn suffered.

That is because al-Hasan declared war mobilization, and then his army moved to the mentioned camps. However, the enemy rumors played an important role in scattering the army. Thus chaos, plots, and treason spread all over it. Accordingly, al-Hasan was unable to wage holy war (jihad) against his enemies. In other words this was the army through which al-Hasan lost hope of winning victory in that war.

From here we understand that Al-Hasan's supporters pledged allegiance to him, and accompanied him to his camps as holy fighters (mujahidin). However, they broke their allegiance to al-Hasan, disobeyed him, and joined his enemies. Thus they were worse than those who had broken their allegiance to al-Husayn before he met his enemies.

In this manner al-Husayn paved the way to fight against his enemies when the events of treason before the battle helped him form the most wonderful army in history in loyalty and obedience though his army was few in number. As for al-Hasan, he was unable to retain supporters even from his sincere Shi'ites. For he was not sure that he would gather them and direct their movements because of the chaos which his enemies spread.

Therefore, isn't there a great difference between their two conditions towards their supporters? The Conditions their Enemies caused The enemy of al-Hasan was Mu'awiya, and the enemy of al Husayn was Yazid b. Mu'awiya. History is full of differences between Mu'awiya and Yazid. For example, the son (i.e., Yazid) had plain dullness, while the father (i.e., Mu'awiya) had a deep viewpoint that the people regard as smartness.

The enmity of these two men (i.e., Mu'awiya and Yazid) towards al-Hasan and al-Husayn did not result from an accidental condition. Rather it was a past historical enmity between banu Hashim and banu Umayya. The Umayyads did not match the Hashimites one day. Rather the Umayyads showed enmity towards the Hashimites, for the former feared that the latter would take their authority.