The death of the Prophet Muhammad in 632 AD prompted a new wave of Muslim conquests
across the region. The Rashidun Caliphate, established by Muhammad’s close friend, Abu Bakr,
was the first to continue the Islamic conquerings across the Middle East and the Mediterranean.
When Muhammad died, Abu Bakr became his successor, although not as a prophet. The prophethood is said
to have ended with Muhammad, but Abu took the title of Caliph in his place at the agreement of
the Muslims of Medina. After Abu, Umar, Uthman, and Ali maintained the Rashidun Caliphate and
embarked upon new missions to spread their power and faith across the region. During the first
caliph’s reign, some of the displeased Arab tribes engaged in the Ridda Wars, or Wars of Apostasy,
with the caliphate’s troops. Following Muhammad’s passing, a handful of the tribes had broken ties
with the caliphate, stating that their allegiance to Muhammad was purely a personal loyalty,
and some of the tribe’s leaders went as far as claiming to be the prophet’s successor in
prophethood, which sparked the discord. Although the conflict did require military engagement,
Abu and his men were quickly able to suppress the rebellions through both war and diplomacy,
and consolidate their power over the Arabian Peninsula so they could shift their focus outward.
The conquests of Iraq and Syria then began during the end of Abu’s reign. When a local Arab chief,
Al-Muthanna ibn Haritha, informed Abu of the potential success his caliphate could have if
they were to target some of the Iraqi territories, as he himself had just achieved, the caliph sent
Khalid ibn al-Walid, his best commander, to see what could be done. At the same time, in 633,
Abu sent another set of troops into Syria with the same goal, and both missions rapidly escalated
from simple raids to full-blown conquests. Abu eventually called on Khalid to reroute to
Syria as the Rashidun troops inched closer to facing retaliation from the Byzantine Empire,
who had recently seized power in Syria. While the Byzantines vastly outnumbered the Muslims,
the latter showed their military superiority just as they had done back in the days of the
Prophet Muhammad. The Muslims, with Khalid at the head, numbered around 20,000, and the Byzantines,
under the command of Emperor Heraclius’ brother, Theodore, totaled somewhere between 40,000
to 60,000 troops. Even so, the Muslims swiftly redirected their men toward Ajnadayn,
where they had heard that the Byzantines would be. One of the main reasons that the Byzantine
troops were surprisingly easily routed may be the fact that they had expected only to be fighting
against a small formation of local Arab tribes. Byzantine sources widely downplay the results of
the Battle of Ajnadayn, meanwhile, Muslim sources recall the decisive victory potentially a bit too
overenthusiastically, claiming the Byzantine side lost around 50,000 men by the end of the struggle.
Either way, only a few months after the conflict, Abu Bakr died of natural causes and was succeeded
by Umar. Despite Khalid’s heavy participation in the triumphant fight against the Byzantines,
the new caliph chose to replace him with a fresh military commander,
Abu Ubaidah. Ubaidah was made governor of the now conquered Syria, on top of taking
Khalid’s position. The Muslims then took Damascus in the same year, defeated the
Byzantine garrison at Palestine the following year, and took Emesa in 636. By this point,
the Byzantine Emperor, Heraclius, was furious and ready to put an end to the Rashidun expansion.
Once again, the Byzantines remarkably outnumbered the Muslim troops. A united force of Greeks,
Armenians, Georgians, Franks, Slavs, and Ghassanid soldiers fought for the Byzantines,
commanded by Theodore Trithurius, the state treasurer and military commander, alongside Vahan,
the Byzantine field commander. The superior Byzantine numbers came to around 40,000, whereas
the Muslims still had around 20,000 to 25,000 men. The Rashidun forces consisted of their own troops
that had previously been split between Caesarea, Palestine, and Jordan, in addition to new men
sent from Medina to provide reinforcements. The situation became more complicated on both sides
as the Byzantines attempted to line up their attack with one from their allies of the Sassanian
Empire, meanwhile, Ubaidah, who lacked proper expertise and confidence, relinquished command of
the Muslim troops back to Khalid, who had clearly already established himself as a well seasoned
and victorious commander. Khalid quickly led his forces to a plateau beyond the Yarmouk River that
he believed served as the best position for the Rashidun army. The Byzantines, in the meantime,
grew impatient with the Sassanids, who insisted that they were not yet prepared to aid their
allies, and decided to move forward on their own. Initially, both the Muslims and Byzantines were
open to compromise, and negotiations went on for roughly three months. While this delay allowed
the Muslims to receive more support from Medina during the wait, both sides eventually became fed
up with the anticipation and prepared for battle. The larger Byzantine army spread their front line
across roughly 13 kilometers, which caused the Rashidun troops to attempt to reach the same span,
despite the fact that they were only able to fan a thinner front line out to 12 kilometers.
Both sides possessed an infantry made up of smirkishers and melee fighters, although the
Byzantines also had heavy troops while the Muslims instead utilized more skilled and
mobile hand-to-hand combatants. During the first day of fighting, a series of individual duals took
place to open the battle, according to tradition, and the Muslim warriors were triumphant. Vahan,
wishing to turn the tide in Byzantine favor, commanded a small portion of his troops to move
forward and examine the Rashidun front line for weakness, but by the end of the day’s skirmish,
the Byzantines retreated. Not yet willing to give up, Vahan thought up a new strategy to
ambush the Muslims during their morning prayers the following day. Khalid, all too experienced,
anticipated a Byzantine surprise and sent scouts to patrol ahead of the rest of their
troops. When the opposing men crossed paths, Vahan ordered his troops to attack anyway, in spite of
the Muslims’ preparation. The Byzantines initially overwhelmed their adversaries,
forcing them to fall back to their camps, at which point the Rashidun women are said to have
shamed their men back into battle as Khalid came to his troops’ aid with reinforcements.
For the following two days, the Byzantines continued to put pressure on the Muslim lines,
but Khalid and his strategic orders kept them at bay. By day five, one of the Armenian field
commanders on the Byzantine side sued for peace, and Abu Ubaidah was eager to comply. Khalid,
however, had quite a different idea of what would come next. He quickly shot down the offer of peace
and began to prepare his men for a full-forced assault the subsequent day. After nightfall,
Khalid sent a group of his cavalrymen to block the only escape route for the Byzantines, which would
have been across a bridge on the Ruqqad wadi. The actual conflict began again with a dual, this time
between a Byzantine commander and Ubaidah himself. The latter was victorious and the Muslims took
that as their cue to restart the full battle. Khalid and his troops wasted no time gaining the
upper hand against Vahan and the Byzantines, and in a short duration, the imperial army was forced
to try an escape, completely unaware that the Rashidun cavalry had made such a task impossible.
The Byzantines were ultimately decimated as they fled and the Muslims were again triumphant,
facing only around 4,000 casualties themselves. With this victory, the Rashidun Caliphate could
claim complete power over the Levant and the Arabian Peninsula. Shortly after, the Holy
City itself, Jerusalem, agreed to surrender to the caliph in 637 after being promised safety
if they did. As for the heroic Khalid, his brilliant efforts went beyond unappreciated.
When he returned to Caliph Umar, he was discharged from all duties and Umar stated that
it was simply God who had brought the Muslims’ triumph, not Khalid and his tactics. Still,
despite encouragement to do so from his peers, Khalid refused to rebel against the caliph
or retaliate, and instead retired in peace. From the time of the Prohpet Muhammad’s death
to the discharge of Khalid, the Muslims had spread their power, and religion,
from Medina to across the Arabian Peninsula and the Levant, and were nowhere near done
expanding. Khalid, before retirement, had already led campaigns through Anatolia and Armenia, and
during the reign of Caliph Uthman, all of Armenia was taken under Muslim control between 653 through
655. One of the main
reasons why the Rashiduns likely had repeated and decisive success in their early conquests
was due to the oppressive Byzantine Empire that had held the lands they wished
to take. Locals were not all that displeased by the prospect of an invasion due to the possibility
of being freed from the Byzantines. Many Iraqis and Syrians even joined ranks with the Muslims
and were eager to assist them in their conquest. Additionally, despite Caliph Umar’s refusal to
acknowledge it, Khalid’s military genius and skill played a crucial role in the rapid Muslim success.
Without his experience and strategy, the Rashidun side may have been more likely to feel the effects
of the Byzantines’ numerical superiority and more advanced equipment. Nonetheless,
the Muslims proved their impressive ability by the end of Khalid’s time leading their armies,
and they were in a favorable position to continue expansion across the Middle East and beyond.