companion of Muhammad. He is noted for his military tactics and prowess, commanding the forces of Medina under Muhammad and the forces of his immediate successors of the Rashidun Caliphate, Abu Bakr and Umar ibn Khattab. It was under his military leadership that Arabia, for the first time in history, was united under a single political entity, the Caliphate. Commanding the forces of the nascent Islamic state, Khalid was victorious in over a hundred battles, against the forces of the Byzantine-Roman Empire, Sassanid-Persian Empire, and their allies, in addition to other Arab tribes. His strategic achievements include the conquest of Arabia during the Ridda Wars, Persian Mesopotamia and Roman Syria within several years from 632 to 636. He is also remembered for his decisive victories at Yamamah, Ullais, and Firaz, and his tactical successes at Walaja and Yarmouk.