634
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638
Abu Ubaidah ibn al-Jarrah

Abu Ubaidah ibn al-Jarrah, fully Abū ‘Ubaydah ‘Āmir ibn ‘Abdillāh ibn al-Jarāḥ, was one of Companions of the Islamic prophet Muhammad. Mostly known for being of one the "Ten Promised Paradise". He remained commander of a large section of the Rashidun Army during the time of the Rashid Caliph Umar and was on the list of Umar's appointed successors to the Caliphate.
Arab conquest of the Levant
The Muslim conquest of the Levant or Arab conquest of the Levant occurred in the first half of the 7th century, and refers to the conquest of the region known as the Levant or Shaam, later to become the Islamic Province of Bilad al-Sham, as part of the Islamic conquests. Arab Muslim forces had appeared on the southern borders even before the death of prophet Muhammad in 632, resulting in the Battle of Mu'tah in 629, but the real invasion began in 634 under his successors, the Rashidun Caliphs Abu Bakr and Umar ibn Khattab, with Khalid ibn al-Walid as their most important military leader.
Battle of Ullais
The Battle of Ullais was fought between the forces of the Rashidun Caliphate and the Sassanid Persian Empire in the middle of May 633 AD in Iraq, and is sometimes referred to as the Battle of Blood River since, as a result of the battle, there were enormous amounts of Sassanian and Arab Christian casualties.
Battle of Bosra

The Battle of Bosra was fought in 634 between the Rashidun Caliphate army and the Byzantine Empire for the possession of Bosra, in Syria. The city, then capital of the Ghassanid kingdom, a Byzantine vassal, was the first important one to be captured by the Islamic forces. The siege lasted between June and July 634.
Military conquests of Umar's era

Umar was the second Rashidun Caliph and reigned during 634-644. Umar's caliphate is notable for its vast conquests, aided by brilliant field commanders, he was able to incorporate present day Iraq, Iran, Azerbaijan, Armenia, Georgia, Syria, Jordan, Palestine, Lebanon ,Egypt, and part of Afghanistan, Turkmenistan and south western Pakistan into the empire of the Muslims. All of these were permanent conquests. The Byzantines lost more than three fourths of their territory and in Persia, the Sassanid empire ceased to exist.
Rashidun Caliphate
The Rashidun Caliphate was the first of the four major caliphates established after the death of the Islamic prophet, Muhammad. It was ruled by the first four successive caliphs (successors) of Muhammad after his death in 632 CE. These caliphs are collectively known in Sunni Islam as the Rashidun, or "Rightly Guided" caliphs. This term is not used in Shia Islam as Shia Muslims do not consider the rule of the first three caliphs as legitimate.
Rashidun army

The Rashidun army was the core of the Rashidun Caliphate's armed forces during the Muslim conquests of the 7th century, serving alongside the Rashidun navy. The Rashidun army maintained a high level of discipline, strategic prowess and organization.
Khalid ibn al-Walid

Abū Sulaymān Khālid ibn al-Walīd ibn al-Mughīrah al-Makhzūmī, also known as Sayf ullah al-Maslūl was a 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.