An Alternate History Scenario I Liked (And Contributed To)

The members of my alternate-history forum whose handle is Eurofed likes larger and larger states, I believe on the grounds that internal stability over larger areas promotes economic development and human welfare.  To that end, he has devised various alternate timelines featuring this, some featuring this unification done by the good ("The United States of the Americas and Oceania"--the U.S. includes Canada from the get-go and grows from there) and the very bad ("The Long Night Falls," a victorious Third Reich uniting Europe and the Middle East).

This one, however, is my favorite

Europe of the Three Empires

Basically, the Roman Empire expands even more than in our history, incorporating Mesopotamia and reducing Persia proper to vassalage and expanding deeper into Europe, giving them a more defensible border (the Oder is shorter than the Rhine and can tie into the Danube as a barrier).  Eventually the enlarged Roman Empire splits apart due to religious and cultural-linguistic (Latin/Greek) differences and a third empire emerged in Russia and Scandinavia based on the Norse, the Goths, and various steppe influences.

There was a lot of discussion about just how big the Roman Empire could get and stay functional.  Geography is one problem, as is the slow speed of communications.  Eurofed is not a believer in geographic determinism--he said India remained disunited even though it doesn't have a lot of division-encouraging geographical features.

My handle on the board is MerryPrankster and I posted a lot of suggestions, including how the Norse and Western Romans would divide up territory (I favored the Norse taking Britain), how the East-West political split might happen, and the East-West religious split might develop.  In particular, if we're going with a Christian East that develops our history's religious-authoritarian Byzantine political culture and a pagan West that is comparatively freer, I figured there'd at least be some Christians who would believe a state church to be an abomination and oppose brutality and tyranny being done in the name of Jesus.

Our history, after all, saw one person of note in the early church (for some reason I'm thinking it was Arius of Alexandria, founder of the Arian heresy) who claimed Constantine did not scourge the back but tickled the belly and "damned the soul with gold."  Not to mention the Biblical justification for imposing Christianity and "Christian" political positions by force on society as a whole is somewhat lacking--when Paul told believers to pray for kings, it was so that they would become Christians and thusly not persecute Christians anymore, not to impose Christianity on everyone with the sword.

Maybe I'll try to write fiction set in something similar to this world, but that would require having an actual plot (for the fiction) and an actual timeline, starting with a divergence from our history.  I suggested some of the conquests be made during the Republican period, since the Republic was actually more aggressive than the Empire (the Emperors wanted to avoid war when possible to avoid having victorious generals threaten them) and more inclined to keep conquered territory.

Perhaps Caesar doesn't get assassinated and sets off for his war against Parthia?  He can get assassinated later, maybe if he goes on a power trip after beating the Parthians and makes himself king (or people think he will try to make himself king), and we can still have our world's Augustus.