Roman (?) Mesopotamia Pt. 2: Some have pointed out that if Rhomania focused on Mesopotamia, it could hold it. I’ll concede that, but here’s why that would be a really bad and harmful decision to make for the Romans.
Let’s say the Romans decide to focus on holding Mesopotamia. What makes you think the rest of the world will cooperate? The Romans don’t know that their western border is secure and that Theodor was the last existential threat from that quarter. They can’t know that and can’t take the risk. If they decide they’re safe from Europe and throw all their forces into Mesopotamia, that action will, by consequence, make them unsafe from Europe.
Let me explain.
A Roman army marches into and seizes Mesopotamia for the purpose of holding it. The Turkish population, the majority, is absolutely not going to be loyal. The Shia Arabs might, but that is not guaranteed, and they’re a minority and concentrated in the south that is the region hardest for the Romans to hold because of distance.
So there’s 2 choices. One, destroy or expel the local populace. Leaving aside the humanitarian horror, the tax base is wiped out. And the source of supplies for any garrisons. So all the material and supplies for said garrisons needs to be transported from the original themes. This will really not be cheap. New settlers can be brought in, but that’s more expense and because there are no local resources they’ll also need to be supported at great cost by the original themes. Meanwhile the survivors of Generalplan Ost are in Persia, dreaming sweet dreams of vengeance and waiting for any signs of weakness and despising all thoughts of peace.
Two, keep the local populace in place and control them through garrisons. If Mesopotamia has 3-4 million people, to keep them in line by modern counterinsurgency standards that would require 30-40,000 Roman troops. And because they need to control the countryside, they need to be spread in small detachments, which means if any Persian field army comes sweeping out of the east, said Persian field army is going to gobble up these Roman troops like so many bite-sized snacks.
Which means another Roman field army needs to be here to protect the counterinsurgency forces. And because of the distance from the original themes and ensuing delay in reinforcements, the Roman field army needs to be big enough to stand up to the might of Persia for at least a couple of months. So that’s at least another 30-40,000 Roman soldiers, and frankly that’s cutting it dangerously small. Because while the Persians are invading, the COIN forces still need to be at it, so they can’t reinforce the field army.
Therefore the minimum to control and defend Mesopotamia requires 60-80,000 Roman soldiers. Now some of these could come from kastron troops, but the various Mesopotamian kastra need garrisons too in addition. Meanwhile the current Roman peacetime army roll is 135,000. So Mesopotamia, by itself, is using up half to two thirds of the entire Roman army.
Aside from the heavy expense of supporting the Mesopotamian defense, there will be opportunity costs Rhomania must pay. A possible pro-Roman German prince contending for the HRE crown can’t be supported because the reserves are in Mesopotamia. The Arletians can’t be supported against the Triunes because the reserves are in Mesopotamia. A major ground force can’t be sent against North Africa because the reserves are in Mesopotamia.
Rhomania’s contemporaries will also notice the commitment and how it ties down the Romans. Would-be allies won’t look to Rhomania because they’re too busy to be a source of aid while foes of Rhomania will be emboldened. The Hungarians will know the Romans won’t be able to protect them from a revived HRE if half to two-thirds of the Roman army is months away, so in the interests of their own safety they’ll flip to the Germans who have their whole army right next door. Serbia and Vlachia will be making the exact same calculations. And the Germans will be looking at Theodor’s old plan, which no longer look insane but visionary. And if the Romans march the Mesopotamian army back west to repair the collapse of its European frontier, then Persia swoops in and takes it while they’re away, in which case all the expense was for nothing.
The Romans could expand their peacetime military, but that costs money, lots of money. Armies are not cheap and not even Rhomania’s coffers are limitless. And the White Palace would really like to not be spending 80%+ of its annual budget on the armed forces. Rhomania can boost it up to 300,000 in wartime, but that’s a temporary wartime measure, not a sustainable permanent peacetime level.
As for the idea of Rhomania just having some forward citadels like Baghdad or in the Zagros as roadblocks, well there’s defense in depth and spreading oneself too thin. This is the latter. The forts need garrisons which need to be fed, which means the countryside needs to be controlled to keep them supplied. Queue all those troop commitments I mentioned earlier.
Also forward positions that are so far forward that they can’t be supported aren’t an asset; they’re a liability. A garrison there will know that if they’re attacked, there’s no chance they can be relieved in time. So their choices are:
A) Fight a battle to the death and die as a glorious speedbump.
B) Surrender. In which case do it early while the terms will be good.
Putting men and material in positions where they can’t hold if they are attacked means that said men and material have effectively been thrown away. Instead they could’ve been used to garrison positions that actually could’ve held until relieved. Except now those won’t hold either, because they’re undermanned or underequipped because all the stuff went to the too-far-forward posts. Plus there are all those nice fortifications that have been gifted to the Persians, which now the Romans would have to besiege if they wanted to take them back.
All of this above is predicated on an intact Persia. Rhomania could try to smash or neuter Persia, and it could get away with it at least once. But Roman ability to project power sustainably in Persia is even less than in Mesopotamia, because Persia is even further away. Once the Romans left, Persia would start to coalesce again. Which again leaves the Romans two options.
1) Let it. In which case in a generation or two Persia is back again, and who knows in what form. Could be better or could be worse. After all, consider what happened after Khusrau II. The Sassanids got smashed, and then the Romans got the Caliphate instead.
2) Periodically send expeditions in to re-smash or re-neuter Persia. Except that costs a lot, not only in direct expense but in opportunity costs. While Rhomania is busy doing that, it can’t do X or Y. Also in doing so, the Romans are really alienating the Persians. Which means at some point when (not if) Rhomania is too distracted by other affairs to keep this up, Persia will re-coalesce, and it will be in a really bad mood.
Now let’s look at trying to hold northern Mesopotamia only. It’s much smaller, lightly populated, and closer to Rhomania proper. Meaning, leaving aside the moral horrors, that’d be much easier and cheaper to remove/destroy the local population and replace them with loyalists. Which means that tons of troops don’t need to be tied down in COIN operations. And since it’s both further away from Persia and closer to Rhomania (so a double bonus), there doesn’t constantly need to be a giant field army about because the region can be reinforced rapidly. The three eastern themes can all get troops here comparable to or even faster than a Hamadan-based power.
Money will still need to be spent on kastra, but all that money that would be spent on the Baghdad kastron (and then lost because it’s too far forward to be supported) can instead go to the Mosul kastron. And that one is in a position to be supported because, again, it’s noticeably closer, so the garrison of that will be more inclined to fight out it because it doesn’t look like they’ve been sent to a suicide posting.
Rhomania still gets a buffer zone for Syria and Eastern Anatolia (which is the point of the whole exercise), but it’s a buffer zone it can reliably defend without breaking the bank or posing massive opportunity costs for Constantinople.
