Ali's Persian War (Fidem Pacis)

In the 630's AD, shortly after the death of the Prophet Muhammad, the Persian Empire took advantage of unrest among the newly unified Arab tribes and attacked the Beni Lakhm who lived on the southern shore of the Euphrates. Khalid ibn al-Walid, the finest general the Caliphate had to offer, led an army to assist the Lakhmids, but only succeeded in provoking a full-scale war. Though Khalid was able to save the Lakhmids, while he was occupied a second Persian army invaded Bahrain and began the process of recovering it as a Persian province.