 Complete the following phrase:  While the Byzantine Roman and Sassanid Persian empires were both weakened by the ByzantineSasanian War of 602628, a new power in the form of Islam grew in the Middle East under Muhammad in Medina. In a series of rapid Muslim conquests, the Rashidun army, led by the Caliphs and skilled military commanders such as Khalid ibn al-Walid, swept through most of the Middle East, taking more than half of Byzantine territory in the 