Conversation so far:
What happened during the reign of Yazid?
He immediately instructed the governor of Medina to compel Husayn and few other prominent figures to pledge their allegiance.
What else was Yazid doing during his reign besides instructing people to pledge their allegiance?
Husayn, believed that Yazid was openly going against the teachings of Islam in public.

Question: How was he going against the teachings?
Self-contained rewrite: How was Yazid going against the teachings of Muhammed?