Answer
Yazid I, the son of Muawiya I and the second Umayyad caliph, faced opposition from Abdullah Ibn al-Zubayr, who claimed the caliphate for himself and refused to recognize Yazid's hereditary succession. This conflict led to the Second Fitna, or civil war, within the Muslim caliphate, with Ibn al-Zubayr establishing his rule in Mecca and challenging Yazid's authority over the rest of the caliphate.