Ridda wars
After the end of the Ridda wars in the Arabian Peninsula, Abu Bakr sent four armies to the Levant, led by Yazid ibn Abi Sufyan, Abu Ubaidah ibn al-Jarrah, Amr ibn al-Aas, and Shurahbil ibn Hasana. Because of the strength and size of the armies of the Byzantine Empire, Abu Bakr ordered Khalid ibn al-Walid to march with half of the Iraqi army to the Levant and command the armies there.