You describe 2 Different spans for the Titanic Cold war between " Lithuromanians " and "Saxonians " , however ; in the history You write that : " after the war of the Scottish succession - which happens in Mid 16 cc - the 2 powers remain locked in the conflict for the next 100 years. " , yet in Your Opening comment ; It's said This story is set in 1748 and They've been at a Stale-mate for the past 80 years - which would place the war's start around 1668 , meaning ; either the " Great confrontation " paused for Several decades before flaring up again , or You simply skipped half a century , and ; in a world where communications , Supply lines , & Dynastic claims evolve on a Predictable schedule , a 50 years slip creates confusion about what Actually happened when & where , which in turn ; Under-mines the Very Stale-mate You invoke as the setting.
You introduce ? , helena ivanovna ; purportedly a Russian princess , as queen of this New union , spark a Russo-polish war resulting in muscovy's subjugation , however ; russia in the late 15 cc was only just emerging from Mongol suzerainty and that the idea that She could produce a Dynastic bride with the prestige to sit on a Now-unified Polish throne - and then be used as a Casus belli to overthrow Muscovy - is such a Radical departure from Logistical & Political reality that It reads less like a Plausible Alternate reality and more like a statement against being sequitur.
In OTL , Asia minor was the Core Heart-land of the Ataman beylik which , especially after 1453 , quickly consolidated power in Asia minor , moreover ; regarding the mamluks from egypt & syria , They've never gathered an invasion force capable of Sustained occupation that Far north , as Their Logistical lines couldn't have supported campaigns across rugged terrain while fending off Barbarians' Counter-attacks , that is to say : at best They might harass Some Coastal cities or border , but Full annexation - complete with retention of Supply networks , garrisons , taxation & administration - is Simply unrealistic.
Polish forces taking the balkans Out-right after the 5ᵗʰ Ottoman-polish war and moving Large armies over the carpathians & danube , through Hostile Mountain passes , and then not only stopping at that but conquering - & holding - territories as varied as serbia , bulgaria , & greece would have required a Logistical & Naval capability that no Central European state possessed in the Early 16 cc , and ; I don't say this to belittle You but even the Ataman empire , at It's Golden age , struggled to control the Remote High-lands , therefore ; Polish-based armies simply lack the Organizational infrastructure to accomplish that.
There's no " Theodosiopolis " in the balkans , that is - Dear sir - Out-right False information.
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Misc :
Also It's important to note that Gaelic ireland's Social & Legal structures were distinct from the scots' , ergo ; there was no precedent for installing a Purely Irish Clan chief as the High king of scotland , especially when You add a Decisive victory on English soil - i.e./ the Battle of Leeds - rather than on Scottish territory. You repeatedly refer to " North umbria " as if It were the Historic Northern region of sexonia , however ; I must correct You as the the Medieval kingdom You may want to call is named " Northumbria " , because " Umbria " is in Central italy and not sexonia. Ireland in the 15 cc was fractured - and I don't mean just Politically , but linguistically & culturally , too - between Gaelic irish clans & Hiberno-norman lords , that is to say : even the concept of " the ireland " as a Political structure was Extremely loose , if not non-existent , ergo ; efforts to unify such a mess would have faced Extreme resistance from both Native clans & the established Anglo-norman settlers. I , nonetheless , thank You for sharing this creation of Thine with Us , and wish You a Pleasant day.