Based on L. Sprague De Camp's "Lest Darkness Fall"
In the end, Martin Padway failed to bring about a full-blown scientific revolution: scientific revolutions require new ways of thinking as well as accumulated knowledge, and Martin, an archeologist rather than a historian of science, did not succeed in changing enough 6th-century minds in 20th century minds for the technological revolution he began to become self-sustaining. His post-death canonization did not help, either: science would evolve only slowly and through many reversals and setbacks.
Although after innumerable trials and failures he succeeded in producing high-quality gunpowder, and further trial and error (and a lot of fatalities from explosions) finally produced good cannon, attempts at individual hand-held weapons remained somewhat iffy at the time of his death. As for the steam engine, the limits of 6th century engineering combined with Martin’s somewhat shaky ideas as the physical construction of such a device insured that steam-powered machines remained no more than toys for generations to come, in spite of his voluminous writings on the possibilities inherent in steam-powered ships and trains: the first steamboat would not chug along the Tiber until a century after his death.
Thanks to the compass and a good notion of what they would run into, ships from Europe would soon be visiting the Americas, but the limitations of ships built for Mediterranean climes in the North Atlantic meant that travel between the continents was long limited to certain times of the year and risky even then: colonization was a slow process.
With gunpowder weapons, the Western Empire expanded at the expense of the Franks, as did the Eastern at the expense of the Persians. Of course, the battle for All The Marbles was inevitable, and after twenty years of horribly bloody warfare a unified empire briefly extended from the Tagus to India, before falling apart under its own bulk compounded by religious warfare.
(Martin’s well-intentioned efforts to introduce religious tolerance cut no dice with 6th century minds, and various of his writings were “interpreted” to show his true belief in Christian Orthodoxy A, B and occasionally C or even D.)
The schools and universities and correspondence associations founded by Padway survived after his death in 570, if albeit often in rudimentary form, and often more interested in relentless study of his works to find the Truth rather than in the original thought and experimentation he had urged (and, even when experimentation took place, it often was used to confirm pre-existing ideas rather than to investigate new ideas).
Still, knowledge inched forward. Encyclopedias of knowledge were still written, people still argued about the nature of matter and the universe as well as angels on pins, and even though some were burned at the stake for insisting Padway had been quite literal in his late writings on the stars and planets, people still looked at the sky with telescopes. Crude microscopes and printing presses and basic sanitation and germ theory (which eventually led to severe overpopulation and famines), basic chemistry and atomic theory and physics – the materials were there, even if the technique was still crude to the point of near nonexistence.
Three hundred and fifty years went by.
In the year 920, the Roman Empire remains disunited, divided between the Western Latin Empire of Iberia, Italy, NW Africa and south-central Gaul: the Eastern Greek Empire in the Balkans and Anatolia and Caucasia: and the Southern Coptic Empire in Egypt, Nubia, Libya, Syria and western Arabia. Lesser powers of the Christian West include the Saxons of England, the African Axumite Empire, the Magyar Empire in the Ukraine, (The Bulgars ended up in what OTL would be Hungary: and then the Eastern Romans ate them) and the Eastern Franks east and north of the Seine, which after their breakaway from the Western Imperial sphere expanded eastwards against gunpowder-free Saxons and Slavs, and in the 700s brought Christendom to Scandinavia with Fire and the Sword.
Christianity remains divided: aside from the three major favors of Christianity in the west, there is also the Manichean-Indian Heresy, a new “truthier” faith proclaimed by a prophet living in the troubled borderlands of Hindu India and Christian Persia in the 750s. Said religion spread rather energetically by Fire and the Sword: although stopped in the west by the better-organized and technologically more able Eastern Romans, it overran Persia and much of northwestern India, a conquering horde dropping railroad tracks behind them, and spread to the borders of China and west to the Volga over the next century and a half. Currently, the Holy Dominions are consumed by civil war, which has allowed the Eastern Romans to re-conquer Mesopotamia. (The Persian plateau had a brief interval of independence).
The Americas as OTL were European-settled: although settlement was initially slower and patchier than in our world, an Amerindian population less dense than in 1492 and just as vulnerable to Old World diseases was still decimated: although sizable Mestizo populations exist along the Mississippi and elsewhere, only the Maya in their jungles and the Tiahuanaco in their mountains were able to resist or beat back conquest, although both ended up converting to Christianity.
The bulk of the Americas have been colonized by the Latin Empire, although the Saxons carved out their own territories in what OTL would be the Guyanas and North Brazil, and the Franks took roughly Canada and New England. The most important overseas provinces of the Latin Empire are centered in Mexico and the Mississippi river basin: as new political ideas ferment and the population of Latin America (hah!) approaches that of the Old World territories, rebellion begins to stir. Rail and radio so far hold together vast and relatively lightly populated areas, but the Emperor is pretty far away in the mountains of deserts of the interior. The discovery of oil has led to considerably greater attention to the formerly somewhat neglected area of what in our world is Venezuela.
East of what in our world would be Poland, several Slavic states have emerged under the pressure of the Frankish March to the East and the influence of the Eastern Romans, adopting Christianity: the area is a backwards one, a region of contending influence and mostly poor peasant societies with a thin skimming of modernity on top. The desolate vastness of northern Russia has been settled by Pagan Vikings fleeing the Franks, who have mixed with the mostly Finnish peoples originally there, and the worshippers of Woden-Yawveh has managed to modernize enough that, combined with the inhospitability of their lands, they has so far avoided conquest.
Mohammed was butterflied away, and what would be Somalia and Southwest Arabia are Jewish: retaining close contacts with their oppressed brethren back home, they have managed to emulate Christian technological progress sufficiently to duplicate the feat.
Africa, backwards and disease-ridden, has not been very thoroughly colonized: there are backward Christian states in the Sahel and those parts of the Sudan not incorporated by Egypt, and the backwards chiefdoms of West Africa have formed into states under the influence of Christian missionaries, traders, adventurers and an influx of gunpowder weapons, the primitive herders and subsistence farmers of southern and central Africa hardly seemed worth the effort to conquer: a number of explorers and missionaries have roughly explored the area, and there is a Latin colony in the Cape area (a waystation to India and beyond before the Egyptians built their canal), but the southern half of Africa generally remains in “pre-scramble” mode. Still, there are probably valuable minerals somewhere in there: claims and stakes are being made, plans for railroads drawn up – the explorers are not necessarily doing it just for Faith or Science! Some adventurers have travelled there in hopes of becoming kings: a few have even succeeded. Some entrepreneurs have set up pricy airship tours of mysterious “jungle Africa” from several thousand feet.
India, outside the areas ruled by the Holy Luminous Empire, is divided into Hindu and Christian kingdoms, some of them loosely allied to block further expansion by the Christian heretics. At one time, much of the continent was ruled from one Rome or the other as gunpowder weapons and later steamships smashed the rule of local Rajas: but with the re-fragmentation of Empire and religious warfare, most of India slipped out of European control again. Nowadays, the powerful navies and armies of the western Empire indulge in gunboat diplomacy and political manipulation. Wars with Christians and Manicheans have led to an increased Hindu militancy, but at the same time the complex politics of India has often led to some odd, religion-crossing alliances.
Much of Southeast Asia and the isles, very thinly populated in this era, have been outright colonized by Latins, Franks, and Egyptians: Western Australia ended up being settled by the Yemeni Jews, nobody else wanting it. Much of the area of what OTL would be Indonesia and the Philippines are a mixed-race “Mestizo” area as a result of heavy colonization. Some small buffer states survive in SE Asia between Frankish and Chinese territory.
China is a rather different nation than our China of the late T’ang, let alone early modern China in our world: it is still an aristocrat-dominated society, and although the bureaucracy has expanded greatly, it has been heavily influenced by western notions rather than Confucian ones. The Chinese have been plagued by gunpowder-armed maritime ruffians from the mid-500s, and well-armed religious fanatics on land from the early 800s.
Although the butterflies meant that the T’ang never arose, the Enduring Peace dynasty has had its own glories, and has done a better job of adapting and modernizing than the Qing of of our world: although China has suffered from invasions and humiliations, it has never been forced to question its fundamental nature: indeed, with better weapons it managed to crush the Tibetans, and in the last century has snared the steppe and the lands north to the Arctic in a web of railway and telegraph lines, and has at least managed to hold the Luminous Empire at bay to the west.
The Yamato Realm is a Chinese vassal: recently, the Chinese aided them in their overthrow of their harsh Coptic overlords while the Egyptians were busy fighting the Latins in North Africa. Still, caution and a sense of balance are needed: China remains backwards compared to the western realms, Christians are growing all too common and influential of late, and students travelling to western universities and schools to bring back knowledge often return with odd and dangerous ideas. Foodstuffs from the eastern continents (western, that is, to a European) combined with imported medical ideas have led to a long-running population boom improved farming methods have barely kept up with. There is peasant discontent, and rumors of the apocalyptic Buddha… (Chinese Buddhism has been rather impacted by Christian influences since the 7th century).
Europe, and much of Asia, is fairly crowded. Rights for women have been slow in coming, and even basic sanitation and germ theory will rapidly grow a pre-modern society. Technological growth has not always kept up with population growth over the last centuries, and there have been some nasty famines: currently the Americas and SE Asia provide a relief valve, both for immigration and as a source of food exports, and people are having less children as they move from the countryside to a more industrial and urban society, but the population is still increasing, and Europe and Africa and the Middle East are rather crowded: Italy, for instance, has increased its population more than twelve-fold over that in 535.
In spite of Padway’s efforts to revive democracy, parliamentary government never really caught on, although it has made some headway in the Frankish realm over the last couple centuries and has emerged in a new form in the Latin realm as a modern bourgeoisie has begun to flex its muscle. In the Americas downright democratic ideas have begun to circulate, while in the east growing Greek cities have begun to try their strength against the imperial court. Still, it is basically a world of kings and emperors: the Egyptian Caesar is more absolute a monarch than Louis the XIV, and even the Frankish Volkestaag is no stronger re their king than the Prussian Parliament vs. Kaiser Wilhelm & co.
The bureaucracy is more modern: Martin Padway managed to get a professional, talent-based system going in the western Empire in his lifetime, and with the printing press to help, the bureaucracy from Lusitania to Silla has done what it always tends to grow: grow and then grow further. Although the Emperor in Byzantium is theoretically God’s go-to guy on Earth, he is to some extent a prisoner of the army of officials which crowd the palace complex, bound by the red tape produced by a truly byzantine bureaucracy.
Thanks to Padway’s efforts, the peasantry in the Western Empire have remained mostly free: slavery, alas, was never entirely eliminated, and as in our history the development of tropical crops led to something of a new boom in the practice: the last of the slaves in the Latin Caribbean only became free a couple decades ago, and there remain various forms of “bonded” labor in all of the major Empires, although the treatment of human beings as outright life-long property has largely come to be seen as “unchristian”, and the notion of slavery as an inherent racial condition has never really caught on, perhaps in part to Axum and the large black population of the Egyptian Empire.
The world has finally entered into a “scientific” era: the basic physical understandability of God’s creation through rational investigation is now commonly accepted in the Christian lands and beyond, and organized state-sponsored research is widespread. Still, scientific thinking would seem oddly religious-minded from the point of view of someone from OTL: it is only about a century since the last, bloody Wars of Religion, and the notion of a purely “scientific”, God-free world-view would seem repulsive to most researchers. This sometimes leads to …odd by our standards interpretations of cosmology and geology.
Technology is basically on a 1930s level, with gasoline-powered machinery, steel battleships, propeller-driven aircraft, and radio. Theory is however not quite as advanced: there has been no Einstein, rather several less prominent researchers have slowly closed in on the ideas of relativity from several directions, and the notice of a universe limited by the speed of light has greatly ruffled many religious feathers. Worse is the whole idea of evolution: geology and paleontology, not being subjects Padway put much emphasis on, were slow off the mark as fields of study, and people still trying to digest the notion of an ancient earth are not at all pleased at the whole “descended from monkeys” idea, which is banned as blasphemous in a number of nations. Society as a whole is more religious than OTL’s “west” in the 1930s, although in this dizzying new era of flying machines (well, heavier than air ones: the first hot air balloon ascension was in Padway’s day), submarines, radio, movies, telephones, record players, etc., there is also quite a bit of fiery (and often legally under threat) atheism, new religious and philosophical movements, and the occasional wacky cult imported from Asia. An equivalent of Socialism as OTL has arisen from the pains of early mass industrialization, but it is not an anti-religious force: in this world it is a religious movement (although often fiercely in opposition to establishment religion) which fails to prevent it from being fiercely denounced as a tool of the devil.
Republican revolutionary movements bubble in the Americas, and attract sympathizers in the Latin, Frankish and even Byzantine Empires. Plots begin to be drawn round the newly discovered oil reserves of Mesopotamia and Eastern Arabia. A militant New Imperial movement in the Byzantine Empire talks of regaining the martial virtues of old Rome and the reunification of the empire and does a lot of marching and strenuous physical exercise. The locals around Lake Titicaca flock to visit the construction site of what when completed will be the world’s largest church, built in the local Freakin’ Huge Stone Slabs style. (Now with concrete reinforcement!) A natural philosopher in Ravenna wonders about the inner structure of the atom. An airship flies over an interminable herd of Wildebeest not yet thinned by modern weapons, and people take pictures from the windows. Brown-skinned, frizzy-haired men pray before the Torah near what would never be called Ayers rock. And in a city near what would be Danzig in our world, a Frankish historian, exhausted after a long day of studying primary sources on the ever-mysterious Martinus, suddenly has the wacky thought that will lead to the most controversial book of the 10th century, hey. What if Martinus was a time traveler?