The PoD is that in A.D. 363, Julian the Apostate manages to return victorious from his Persian campaign, leaving Sassanid Persia in a civil war. He has an eventful 30 year reign (barbarians and rebellions and more) that is notably remembered for laying the foundations for a Neoplatonic Hellenism which will become the state cult and intellectual worldview of Rome [1] and that of numerous post-roman polities even after the Empire's fall by A.D. 500. Yes, the Empire doesn't somehow last forever thanks to the success of one emperor's military campaign. The divine Fortuna decreed that Rome shall rise, and She decreed that Rome would fall.
Though Rome would fall, however, this world would not see the permanent end of Rome. Rather, ATL Rome proceeds more like OTL China - that of a Civilization that forms a Universal Empire, prospers, then stagnates, declines and falls, then later reforming into another Universal Empire. See the once mighty Han Dynasty of China, which after a Golden Age, declined and then fell into a centuries-long period of division before the Chinese reunify their Universal Empire under the Sui and Tang. This state of affairs marks much of this world's history. Not just Rome and China, but also Iran, Bharat and other High Cultures [2] will form a Universal Empire which develops then declines and falls and then later reunifies. Such is the cyclical nature of life and history.
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Welcome to a Multipolar World.
It is the early 21st C. The world is divided into numerous civilizations that each develop and interact with each other. These would be the different poles of this multipolar order. By the early 21st C, there are about 20 different poles, in varying degrees of size and development. From tiny Papua to large China and everything in between. In fact, this is quite a diverse world. The people in each of these poles are proud of their cultures, histories and traditions. This is thanks to the lack of a global imperialism that would have framed, for a time at least, the entire world's worldview around the culture of a single pole. This world, by contrast, has native forms of governance and indigenous traditions and values survive and prosper. Global technological changes like industrialism no doubt impacts each of these cultures, but the people of this world adapt to these changes based on their own cultures and values. These cultures are not stagnant, but are vibrant and develop on their own terms. Anything not moving is dead as they say, and the world's cultures are very much alive.
This world sees the thriving of numerous native polities in the New World. The Norse started the contacts between Old and New Worlds and the entire world has never been the same since. These contacts first started in the Viking Age (as in OTL) but contrary to OTL, these contacts never stopped and Norse settlements in Vinland never ended. It is important to understand that these settlements were initially really small and would remain so for quite some time. These settlements, of course, served as excellent points of contact between the peoples of the New World to encounter those of the Old. Disease spread, which was deadly, no doubt, but over time, the native populations rebounded as the diseases were here to stay. Also, the Norse methods of ironworking spread to the natives. The warlike Mexica and Tarascans used these metal tools to great effect in their struggles against each other. Finally, Norse shipbuilding was enthusiastically adopted by the Taíno who formed a loose kingdom-confederacy in the Caribbean whose founder was a warrior-priest-king who worships a syncretic Sun God based on the Norse Sol and the Mayan Kukulcan.
A rising power in this world is the Grand Khaganate, also known as Russia. It's a Nestorian [3] Christian East Slavic-Turko-Mongol polity that blends the best of each of these influences. Naturally, the Russians were an expansionist realm who strove to unite the known world under the Great Blue Sky. Attempts by various dynasties to do so have not met great success, though, but the initial nomadic impulses of the Turko-Mongols were in time replaced with that of the more sedentary agricultural society of the East Slavs. As centuries pass, and after a slow start to industrialism which resulted in socialist [4] reform movements, the Grand Khaganate re-structured as dynasties collapsed and were replaced. Eventually, the Khaganate began to assert its dominance as master of the Heartland of the World Island. It is largely thanks to Russian efforts that much of Eurasia formed an Inter-Civilizational Forum called BRICS. BRICS, which consists of Bharat, Russia, Iran, China and Siam was founded to promote development, stability and safe passage of trade across Eastern Eurasia.
There is also an established power that needs mentioning. This is Bharat. The Bharatis after a prolonged period of warring states were united in a Universal Empire during the 11th C. This Bharati Empire was a large empire encompassing all of South Asia and had vassals across the Indian Ocean. Bharati influence could be seen all throughout the Silk Road and it was in Bharat where the first Industrial Revolution began. This was the closest this world had to a single pole dominating the world, but even in this case, the Bharatis were either unwilling or unable to exert their influence into the New World or in West Africa or Europe. Perhaps it was due to how the Bharatis envisioned their empire - that of a mandala which has a central core under central control, but this mandala radiates outward in ever-decreasing layers of influence. In this worldview, those distant regions were simply left alone. In any case, however, even the Bharati empire collapsed (c. A.D. 1500). Many vassalized regions would later be centres of independent Civilizations as the centuries pass. Of course, Bharat would later be re-created under a new dynasty (c. A.D. 1800).
Much of the world's technology compared to OTL really cannot be compared with OTL. It is highly divergent with some areas more or less untouched by industrialism but some areas could be said to be more advanced than OTL. Examples include public transportation networks [5] and agricultural methods. This would generally be in the developed empires of the world.
As a response to the new challenges brought by industrialisms, some of the larger polities began to engage in greater dialogue with each other which led to the creation of Inter-Civilizational Forums (ICFs) to better promote cooperation and development and to decrease inter-civilizational violence. BRICS is one, as is the Nipponese-led initiative called the Eastern Compact with the developed New World powers of Mexico, Tawantinsuyu and the Taíno.
There is an ICF where each of the world's poles are represented. It is called the "Universal Assembly" but is known by its Greek name because it's based in Alexandria [6]. The Universal Assembly was founded quite recently as the world got more integrated thanks to technological developments spreading all over the world. It is a more informal forum where different poles can discuss the world's most important issues and come up with ways to address them. What some may call "intercivilizational law" was decided upon here, though it is more a diplomatic code than a worldwide constitution.
It's not a perfect world though. War still exists among intra-civilizational polities [7] as these fight for hegemony where large Universal Empires have not yet formed. But it's a world, nonetheless, complete with both challenges and triumphs.
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[1] Christianity will not die out in the Roman Empire. Rather, it would play a role similarly to Buddhism in OTL China. Neoplatonic Hellenism in turn functioning more or less as an analogue to Chinese folk religion and Confucianism.
[2] Used in the Spenglerian sense of
Kultur. On a related note, the term "Universal Empire" could also be replaced with "civilization-state" and the meaning would be the same.
[3] Not technically "Nestorian" as Nestorius would never have been born. Assyrian rite Christianity would be more accurate, though it is more or less the same theologically to OTL Eastern Orthodoxy.
[4] Socialism in this world should not be confused with OTL Communism. It is more a traditional peasant-based reform movement than anything. These movements could be quite radical, though.
[5] Personal cars are more or less nonexistent due to either massive government regulation or because industrialism hasn't really spread to some areas. In more developed regions, most people get around in public transportation, use bicycles or walk. In less developed regions, animal transport is common.
[6] Alexander would be proud, knowing that the entire world gathers in the great city named after him.
[7] Meaning polities within a Civilization. For example, within Nusantara, various Malay and Sumatran kingdoms regularly fight wars with each other.
