summary: Imam Husain (A.S.) faced the deviated Ummayad plot in the Islam and, also, the difficult conditions which the Ummah lived in. He (A.S.) also lived its danger proportions after the signing of the peace document between Mu'awiya and Imam Hasan (A.S.).
Whoever follows the life of Imam Husain bin Ali (A.S.) will deeply realize that his role in Islamic life started very early. While still a young man, he contributed, effectively, to the rising movement of Islam. Eminent was his role during the Imamat of father, the Commander of the Faithful, Imam Ali (A.S.) and side by side with his brother Imam Hasan (A.S.).
In the wake of Imam Husain's (A.S.) departure to his Exalted Lord, Imam Husain's (A.S.) role entered a new phase due to the complications which sprung up in the midst of the Ummah, since the role of any Imam from the house of Prophet Muhammad (S.A.W.), is defined by the nature of the social, ideological and political developments of his time.
Indeed, Imam Husain (A.S.) faced the deviated Ummayad plot in the Islam and, also, the difficult conditions which the Ummah lived in. He (A.S.) also lived its danger proportions after the signing of the peace document between Mu'awiya and Imam Hasan (A.S.). one of the goals figure in Mu'awiya's notorious plan:
1.Unleashing a wave of terror, and embarking on elimination of all opposition forces, particularly the followers of Imam Ali (A.S.). They were hunted down, and every means of oppression and terror was employed to silence every free voice.
source:http://alhassanain.org/english/?com=content&id=605