Justinian's Roman Empire vs. Islam?

Let us suppose both that Justinian's reconquests go better and are retained longer (so they hold onto all of Italy and a good chunk of Hispania), and that Islam bursts onto the scene around the same time. We shall also assume a comparably futile and damaging war with Persia as historically happened. Yes, these are very narrow constrictions.

How might the ensuing wars play out? On the one hand, the Empire has more resources. On the other, they have more to defend. The Arabs would not be the only threat, after all. The Visigoths might likely be holding a grudge, for example.
 
Let us suppose both that Justinian's reconquests go better and are retained longer (so they hold onto all of Italy and a good chunk of Hispania), and that Islam bursts onto the scene around the same time. We shall also assume a comparably futile and damaging war with Persia as historically happened. Yes, these are very narrow constrictions.

How might the ensuing wars play out? On the one hand, the Empire has more resources. On the other, they have more to defend. The Arabs would not be the only threat, after all. The Visigoths might likely be holding a grudge, for example.

If the Muslim Arabs would have appeared when the Justinian conquests are finished, maybe they would have crushed the whole Empire even faster that they partially did IOTL.
After Justinian completed the conquests, the ERE was technically bankrupt and not able to pay soldiers or anything. That's why a B-class Germanic crowd like the Lombards could ransack all Italy with little resistence only three years after Justinian's death. Imagine the Arabs.
If the Sassanids were so successful in the first stage of their wars against the Byzantines it was in part because of the ERE was still recovering from the complete fiscal exhaustion caused by Justinian, which obviously damaged a lot their military force.
Modern historians usually agree that Justinian mortgaged the fate of the Empire with their expensive imperialist plans, and the ERE paid a lot for that during the following century.
 
To be clear, I'm not suggesting that the Arabs might attack early. Basically, just what if, for all the treasure spent to retake the west, the investment was retaines for the intervening century.
 

Deleted member 67076

They'd do better as there'd be no Lombard invasion and thus more troops can be used to attack the Caliphate forces. Possibly might be able to check them in Africa or so.

However, to hold Italy you need the initially invasion to do better. Which is easy. Have Justinian give Belisarius a proper army, not a small one of 15,000 men. That way, he wouldn't be overstretched and have to play whack a mole for years on end. War could be wrapped up by the end of the 540s and Italy wouldn't suffer all the de-urbanization, population loss and turn into a money sink.
 
It'd be pretty bad for the Byzantine Empire. The war with Persia would undoubtedly have generated local weaknesses in Spain and Italy (think of all the Byzantine garrisons there having to be shipped back to Constantinople to hold off the Persian invasion), and that's when you would see the Visigoths and Lombards invading those areas again.

Having more men might not even help in defeating the Persians, considering that the victorious campaigns of Heraclius were conducted by small, maneuverable forces that plundered the Persian rear; and that if the Byzantines had a large army at their disposal the temptation to just conduct a massive (and bloody) thrust across the length of Anatolia must have seemed the more rational choice.

And what then after the Persians had retreated? With local 'barbarians' ravaging Spain and Italy and assuming that these lands are contributing much to the Byzantine treasury, this means that the Empire would have to get those lands back. This means more armies, more men, more taxation. Which means that barbarian rule becomes even more acceptable to the Italians/Iberians, which makes the Byzantines' job even harder.

So by the time the Arabs invade, the Empire is still in the same state as OTL: militarily exhausted, financially bankrupt and locally unpopular. Except now the Byzantines don't just have the Arabs to worry about, they have fronts in Italy and Spain as well. I'm not saying that the Arabs would be able to conquer Constantinople, but I do think they'd be able to take what they have OTL and more, perhaps even initiate the invasion of Spain and Italy several generations earlier.
 
So basically you want to avoid the war with Sassanian Persia that exhausted both empires to the point where neither was really capable of successfully holding off the Arabs?
 
Let us suppose both that Justinian's reconquests go better and are retained longer (so they hold onto all of Italy and a good chunk of Hispania), and that Islam bursts onto the scene around the same time. We shall also assume a comparably futile and damaging war with Persia as historically happened. Yes, these are very narrow constrictions.

How might the ensuing wars play out? On the one hand, the Empire has more resources. On the other, they have more to defend. The Arabs would not be the only threat, after all. The Visigoths might likely be holding a grudge, for example.

The Arabs were lucky at that timeframe. The Arabs were never considered a major threat until they attacked. Both empires were exhausted. Absent of empire exhaustion, Persia and Rome can beat the crap of out the Arabs. Even they lose a single battle, they can keep sustaining the war. Even if we assume the Arabs would have better generals, The Arabs dont have the same resources as either empires. A perfect parallel of the situation is Russia vs Sweden.
 
We're still looking at an exhausted empire in my scenario. Just a larger exhausted empire.

In fact, the difference is slight. Italy was left to its fate excepting some strongholds (Ravenna and so) and Southern Spain was too far to make some difference in resources against the Arabs. The result is more or less the same I guess.
 

Deleted member 67076

We're still looking at an exhausted empire in my scenario. Just a larger exhausted empire.
Then the Byzantines have more resources to keep their core territories in tact. Expect to see more of Italy (likely the Latinum region stays), the Balkaans and possibly Anatolia remain part of the empire in the initial wave of invasions.
 
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