Yazid ibn Mu‘awiyah was an Umayyad caliph who committed uncountable crimes during his short-lived reign. In the first year of his three-year rule, he issued orders that the Prophet's (S) grandchild, Imam al-Husayn (as), must be put to death along with all his companions. The method in which this objective was carried out was so abominable that it gave birth to countless subsequent uprisings against Yazid.
To this day, this despicable action has remained a legitimate cause for constant sorrow and protest, and many Sunni scholars have voiced strong objections against Yazid. Unfortunately though, some biased and extremist ‘scholars' and their narrow minded followers have ventured to come to Yazid's defence and have fabricated writings in praise of Yazid to try to deceive readers about his dark and treacherous role in history.
We will now examine this issue in detail and provide historical evidence to bear witness to the fact that Yazid was the direct instigator of the martyrdom of Imam al-Husayn (as).
source : www.rafed.net