The prolonged Byzantine–Sasanian wars, most importantly the climactic war of 602–628, as well as the social conflict within the Sasanian Empire, opened the way for an Arab invasion of Iran in the seventh century. The empire was initially defeated by the Rashidun Caliphate, which was succeeded by the Umayyad Caliphate, followed by the Abbasid Caliphate. A prolonged and gradual process of state-imposed Islamization followed, which targeted Iran's then Zoroastrian majority and included religious persecution, demolition of libraries and fire temples, a special tax penalty ("jizya"), and language shift.