Those were very interesting threads Elfwine, thank you for directing me to them. I tend to agree that timelines in which a radical personality change of a historical figure is a pivot are problematic. Manuel, being Manuel, lost this campaign due to his lack of caution not his armies' lack of capability (see the Battle of Hyelion and Leimocheir in 1177, in which the Romans inflicted the exact same type of defeat on a Turkish army). If only Manuel had a son who could have pursued a rational policy of reconquest in Anatolia that focused on Castles and re-settlement.
Even without extensive fortification, just a gradual and measured pace based on what the state can support rather than what the mind of the Emperor can imagine as possibilities.
The Byzantines
can fight Turcomen raiders the same way they fought Arabic raiders, but not without a firm base - both on the frontier and at heart.
And Manuel greatly strained that - even if he did have a capable son (like my timeline), said son will be busy.
I particularly thought that your idea of having the Romans exploit the successes of the Third Crusade's crossing of Anatolia and capture of Ikonion was brilliant; if a son of Manuel had say, a 30-40 year reign as his father did, I can see Anatolia, including Cappadocia, Melitene and Antioch returning to Roman rule, albeit with a large Turkic presence. This, combined with the historical expansion of the Georgian Kingdom into Armenia and Azerbaijan could easily tilt the balance of power back into Constantinople's hands on this front.
I think so. It would take a lot of hard work and patience of the sort John II showed more than half a century earlier, but the Turks aren't - yet - so deep rooted as to make it impossible. But it would not be easy or quick. The idea of the pre-Manzikert borders 1200 is going to be in little more than name - even if the empire can defeat Turcoman raiding bands, keeping them from being more than a nuisance will take decades of fortifying, settling, converting (as much as possible), and generally holding on.
But IF Alexius (to use the name I used for my timeline and Manuel used OTL) is able to take advantage of the opportunities, deal with Serbia and deal with Henry VI (Barbarossa's son), the Byzantines are not spent - just in desperate need of a breather after running every which way under Manuel.
A final POD proposal:
1. (diplomatic POD) Manuel allies with the Danishmend Emirs of Eastern Anatolia instead of the Rum Seljuks during the 1150s and 1160s, and thus the Turks are less united, Manuel fails to take advantage of this though due to his failure to focus on a single front and the disastrous expedition to Egypt.
2. (biological POD) Manuel's first wife, Bertha of Sulzbach, gives birth to a son (I will name him Theodore, after the warrior saints) in 1160 who, raised by his pious German mother, becomes John Komnenos redux and more pro-HRE than Manuel. He thus elects to focus upon Anatolia and crusading as his grandpa had done so successfully, perhaps in concert with the 3rd Crusade of Frederick Barbarossa?
3. (tactical POD) Manuel accepts the peace overtures of the Sultan in 1176, as was done in your TL. The Romans defeat the Turks in 1177, and build a third new fortress as Kastromon, continuing a slow advance in Anatolia into the 1180s.
These were the three simplified PODs I was working with for a powerful Komnenian Empire in the 13th century. I am indebted to your Eagle of the Bosporus, and would love to continue that concept into the era of the Mongol invasions and beyond!
The main problem with #3 and #2 is that it's almost inevitable that anyone in the 1180s and 1190s will be very, very busy with Western problems.
Henry VI is an ambitious son of a gun, Stefan is looking for an opportunity to rebel, and Bela wouldn't mind taking back some of the territory Manuel took either.
I'm not saying this makes them bad PODs - but one thing that constantly bothers me as a Byzantinophile is that we like to think of "if this had happened, then the Byzantines would be able to retake Anatolia".
But it's not that simple. It's not impossible, but even with a vigorous, intelligent, prudent successor to Manuel, the Byzantines at the end of the 12th century will are facing the same problem that Alexius I faced at the end of the 12th - there is a
lot to do before progress can be made.
Example of that being ignored:
https://www.alternatehistory.com/discussion/showthread.php?t=34282
Mind, it's not ASB, but . . .
The Emperor becomes more cautious in his old age – he turns 60 in 1178 – and seeks to preserve his gains for his son and raise him as a proper emperor. When Manuel dies peacefully in 1187, he leaves his son Alexius II a full treasury, a strong military, a popular regime and a strong position in Eastern Med politics.
Easier said than done doesn't even begin to do justice to it.
Still, it isn't doomed, and the few specific policies mentioned are probably sound.
Thing is, I'd see Byzantium agreeing to vassalage. The Mongols wouldn't have seen themselves as Roman emperors a la Ottomans.