The Arab conquests brought about the collapse of the Sassanid Empire and a great territorial loss for the Byzantine Empire. Though spectacular, the Arab successes are not hard to understand in hindsight. The Sassanid Persian and Byzantine empires were militarily exhausted from decades of fighting one another. This prevented them from dealing effectively with the mobile Arab raiders operating from the desert. Moreover, many of the peoples living under the rule of these empires, for example Jews and Christians in Persia and Monophysites in Syria, were disloyal and sometimes even welcomed the Arab invaders, largely because of religious conflict in both empires.