WI Eastern Roman Empire is victorious in the battle of Yarmouk in 636 AD

In 15 August 636 a large Eastern Roman army head by Heraclius and several other generals clashed with a much smaller arabian army lead by Khalid ibn Walid.
After a fierce 6-day battle the Roman army was routed having lost almost 45% of its strength while the arab army (despite being severely outnumbered at least by 10 to 1) had way much less casualties.
After the battle Emperor Heraclius with the remnants of his army seeked refuge to Antioch considering a counterattack but he soon realised that he had neither the men nor the money for such an attack... And from there he fled to Constantinople abandoning the Levant which was flooded with arabs for ever.
WI The Roman army was victorious and destroyed the arab army then? Could they retain possession of Levant and subsequently of Egypt (Egypt fell to the Arabs 6 years later).
Could he contained the arabs had he won? Heraclius army was around 40000-100000 mean according to sources while the Arab army was about 25000-40000 men.

I think the Levant is doable, but Egypt is decidedly dicey, it really could go one way or the other, for the Romans. All depends on whether the Monothelite doctrine works out.

Funnily enough, I've just done a map with a similar starting scenario, that is, a world where Islam exists, but is never able to expand. This is how I saw the world as it would be in the year 700.

My guess is that if Levant is secured in 636 then Heraclius might have chosen to fortify Egypt...
Egypt was precious to the Empire since it was its main granary and i tend to believe that Heraclius would be willing to sacrifice Levant (if needed) in order to protect Egypt.
A second option would be to protect both (since Holy Lands were part of the Levant and keeping them would be a huge morale boost for the Empire and the army) but that would mean stretching his army too much and it would weakened the Empire.

Basileus Giorgios said:

Funnily enough, I've just done a map with a similar starting scenario, that is, a world where Islam exists, but is never able to expand. This is how I saw the world as it would be in the year 700.

Click to expand...

Are those Korea colonies on the Japanese islands?

Sumeragi said:

Are those Korea colonies on the Japanese islands?

Click to expand...

They certainly are. Korea-wank caused by stronger Gokturks and a weaker China, that allows Korea to become the premier power of the Far East.

At that early stage, the Arab armies are still very dependant on being successful in battle to reward followers with booty. So ongoing defeats will eventually lead to a collapse of the war effort and Arabs going home.

But it is likely to require more defeats than just Yarmuk unless it is one of those devastating Cannae-like victories. If the victory is followed up on with more Byzantine and Persian victories, then the Arab armies will collapse as some people flee back in the desert and others defect to the Byzantines and Persians. There will be a core of devoted Muslims, but they won't have the allure of victory to attract enough followers to be a significant threat. However, the Arabs have some very good military leaders at this time, so these ongoing defeats are by no means certain.

In short, I think many things are possible. One can imagine a complete victory for the Byzantines that ends the threat of Arab invasion forever, to a scenario that the next battle being an overwhelming Arab victory that more or less restores OTL (in which case, the defeat at Yarmuk is likely mythologized away as Allah chastizing the Muslims for being proud, or simply not mentioned at all except as a minor skirmish) to anything inbetween.

Also the Romans were in a pretty awful position given their past wars against Persia. Even a few years of peace that a victory at Yarmouk would bring could mean the difference between a Roman and an Arab North Africa and Middle East.

Magnum said:

Also the Romans were in a pretty awful position given their past wars against Persia. Even a few years of peace that a victory at Yarmouk would bring could mean the difference between a Roman and an Arab North Africa and Middle East.

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Agree... Heraclius himself saw that too after his defeat when planned a counterattack. Thats why i suggested above that if needed Heraclius might had to ssacrifice Levant in order to defend the Empire's main granary (that is Egypt).