A cooperative effort between QuantumBranching and CyberPhoenix001, who tells me the original spark for the idea of this TL came from an episode of the Colbert Report.
The Ottoman Empire succeeds in conquering southern Italy in 1481, taking Rome in the process. During the Ottoman invasion of Italy, the French take the opportunity to invade and annex Lombardy, Liguria and Piedmont, while the Ottomans take Sicily, Naples and the Papal states. During negotiations at the end, the Tuscan city states manage to negotiate their way to independence. Venice, out of geographic and economic necessity, is forced to become a de-facto Ottoman vassal in the aftermath of the invasion.
When the Ottomans take Rome, the Pope is forced to flee to Avignon and put himself under French protection, while the Ottomans set up a puppet to govern the many new Catholics in the Empire, and to curry favour with the local Italian princes, they make sure to stack the clerical leadership with local family nobles. This drastically alters the religious dynamic in Europe, as there are now two Popes, both under the yoke of a power that do not hesitate to manipulate them to further the causes of their own empires. An alt-reformation quickly gets under way, with a general shift towards centralization of the church within the state, with Kings declaring themselves leaders of their own Churches to avoid having to follow the edicts of a Pope subordinate to a foreign state. Meanwhile, Spain, Portugal and several other states try to recreate the own papacy within their own borders. The ultimate successes of these ventures vary.
This shifts the religious paradigm in the British Isles, and after the Fat Lady finishes her number, Ireland and Scotland are in the same religious club and Britain proper (somewhat screwed over by their Wars of Religion) is in a different one.
The Ottoman conquest of Italy brings in a large influx of wealth and naval experience into the empire, resulting in a shift of policy by the Empire, refocusing it as a more western-focused and more navy-centered system than OTL. With control over the Eastern Mediterranean secure (aside from the Mamluks, but they don't really pose much of a threat: they get conquered a bit later, in the 16th century) the Ottomans strengthen their grip on northern Africa and prop up Granada following its invasion by Spain. Isabella of Castille is killed by an assassin while visiting to boost the Spanish troops' morale, causing the Spanish offensive to collapse, leaving Granada as a vassal (and later province) of the Ottoman Empire, giving them an Atlantic port and access through the Strait of Gibraltar, a position strengthened by their later annexation of Morocco. In the end, Granada does not make it into the twenty-first century; the Ottomans Empire cannot be strong everywhere, and Granada finally falls to Spain while Russian and Hungarian distractions peak, but for a good long while the Ottoman foothold distracts Spain from American ventures.
Christopher Columbus still tries to get finances for his passage to India, but with the Reconquista rather unceremoniously halted and chaos in Spain over the assassination of the Queen, no one is in the mood to finance some mad scheme to travel around the world to India on the basis of some calculations of planetary circumference Eratosthenes would have found fishy. The America therefore go undiscovered a while longer, until the Portuguese make it to the coast of OTL Brazil by accident while on their way to India.
Before this happens, Askia the Great of the Songhai makes his hajj and makes quite an impression on the locals; the Sultan agrees to set up trade relations. With its enhanced naval focus, the Ottomans set out along the coast of West Africa in some new ocean-going vessels. This gives them experience navigating the open ocean and helps strengthen the Songhai, allowing them to weather the hardships that they would have faced in OTL (preempting the Moroccan invasion also helped). Also, the more westward-focused Ottomans never get around to finishing off Hungary, instead moving into Dalmatia to secure the Adriatic, and the canny heirs of Matthais Corvinus manage to establish a working détente with the Ottomans: this benefits both, since the Hungarians use the opportunity to strengthen their power base in Eastern Europe, seeing the HRE as more of a rival than an ally in the region, while the Ottomans have nearly a century free from eastern distractions to carry out their own colonial efforts in the Americas.
The Portuguese, having discovered the Americas (ATL named the Antilles), set up colonies in South America. The Ottomans take notice and set out an exploratory vessel which lands in the Caribbean. Spain, still in very poor shape, is in no position to stop them, and the Portuguese global empire is too thinly stretched to prevent poaching in “their” territories. The current Sultan decides to follow up and sends out a contingent that ends up making contact in Tenochtitlan. The Ottomans are less brutal in their conquest methods than the heirs of the Reconquista, and rudimentary smallpox vaccinations end up preserving a large amount of the Aztec population, along with speeding their conversion to Islam as a side effect. With the “necessity” of human sacrifice ended, the Flower Wars are ended as well. The Ottomans build up a power base in central Mexico from which they expand and a hybrid culture arises.
When other powers come a'knocking, the Ottomans are able to repel them. The colonization continues as a pet project of the Sultans, with Turks, Arabs, Jews, Italians and West Africans all coming aboard to the new land across the sea. With the capital located at a very great distance from the colonies themselves, a form of local authority is instituted allowing the colonies a degree of self-sufficiency from the Old World Empire. Eventually, Ottoman sovereignty becomes largely nominal.
Butterflies lead to Mary of Burgundy avoiding death in a horse-riding accident, and consequently the Burgundian Inheritance is much larger, strengthening the Low Countries region of the HRE. The Hapsburg power base shifts there as a native merchant class rises, backed by the Holy Roman Emperor. They will go on to unite most of Germany under their rule, although it takes a few centuries (and there are those who grumble that the job is still incomplete).
Scotland and Ireland both undergo serious alienation from England, the dynastic union between Scotland and England never takes place, and what in our world would be dismissed as the “Celtic Fringe” becomes what is known as “The United Kingdom” in this TL.
France, which avoids the very messy religious wars of OTL, is the Firstest With the Mostest into South America, and plunders the heck out of the Inca empire. It also (attempting to muscle in on the Dutch/Habsburg markets in Asia) seizes the South African cape and found a colony in the 1600s which expands steadily for some two and a half centuries. Sweden, meanwhile, takes OTL France’s place as colonizer in *Canada and Britain’s place in *New England, and with a relaxed attitude about where it gets settlers from (Norse, Danes, Scots, Irish, etc…) their colony grows like topsy.
French and Spanish relations go rather bad following the Ottoman invasion, given the Spanish view of the French as “jackals to the Ottoman lion”: this is not helped by the fact that each has their own Papacy that claims to be the legitimate leader of Christianity in Western Europe. This hostility extends to the colonial race, with each nation doing its bit to make the other's life difficult.
Russia, facing a stronger Ottoman empire and opposed by a strong Hungary and Sweden in efforts to expand at Polish expense, pushes eastward earlier than OTL, and establishes a permanent position in the Americas. In the 19th century, under an aggressively militarist and nationalist regime, Russia turns west, conquering Poland and Swedish Finland, and threatening Hungary and central Europe, only to be soundly whipped by the French and pushed eastwards again, kicking off two generations of political turmoil.
Poland avoids the “Deluge” of OTL, and when not jockeying for position with Hungary unites for a bit with Hungary in a mega-eastern-European state (which predictably falls apart again in a couple of centuries): it avoids partition, and does better at developing a national rather than a nobleman-based or purely ethnic identity, which allows it to re-emerge from a period of Russian rule with a larger territorial base than OTL.
Italians, unhappy with the choice of being French subjects or Ottoman subjects/puppets, grow enamored of the notion of their own land in the Antilles. Italians initially come to North Antillia aboard French and Ottoman expeditions: later, with funds raised by various groups back home, they form a separate colony in Florida. With North America a patchwork of colonial claims, there is nobody with a clear claim to the place, so they avoid the fate of OTL minor colonies wiped out by the British or Spanish. They then unite under a native constitutional monarchy, forming the Kingdom of Fiore (Italian for flower), with the capital of San Francesco: steady growth over the last two centuries has brought the kingdom’s status from “joke” to serious second-rank power.
South Antillia is colonised by multiple powers, as opposed to just the Spanish and Portuguese as in OTL, and as a result, the colonial race is much fiercer. Portugal obviously has a head start, but they soon come under fire from the other powers. Even the Songhai manage to get a piece of the pie, although their small wedge of territory was to some extent dependent on friendly relations with Portugal (up until they ran out of unconverted pagans to conquer, the Songhai were one of Portugal’s major suppliers of slaves).
Technology advances quicker, as does industrialization. The Italian Renaissance is continued under pro-Italian sultans interested in the new art and learning coming out of their western conquests, and what OTL would be scientific inquiry first gets underway under Ottoman rule. This leads to an Ottoman chemical revolution, followed by the discovery of rudimentary gas theory, with cross-fertilization taking place between east and west. Indeed, an Ottoman engineer even devises the first diesel-powered internal combustion engine around the same time Europeans develop the steam engine. After demonstrating it and extolling its potential capabilities, he receives government funding to develop the technology.
Islamic medical science, as well as personal hygiene, is adopted early on by the European nations, allowing for faster development of vaccines and medications. Unfortunately, chemical weapons are also invented earlier (and are used for longer), under the hideously ironic name “antibiotics”, meaning “anti-life” (biological warfare, on the other hand, is referred to as “pathogenic warfare”). Also, the Ottoman monopoly over the oil does a lot to spur development of alternative energy in the 20th century.
Working mechanical computers (not too dissimilar from the Babbage Engine of OTL, but on a smaller initial scale) are developed in Europe by the mid-19th century, and from there spread to the Ottoman state. The origin of the ideology of Technocracy is rooted in the arrival of these mechanical computers and other early “information tech” in the Ottoman state in the late 19th century. As it streamlined and revolutionized the bureaucracy managing the workings of the Empire, people began to foresee the day when human error could be entirely removed from the workings of government by the machine, and began making calls to replace the government with machines, or at least the people who operated the machines, namely scientists and engineers.
As the political clout of the scientists and engineers grew, so too did their criticisms of the current administration. If humanity is to truly form utopia, they said, it can only be at the hands of the wise, the intelligent, and above all properly trained and educated. This anti-democratic sentiment tied together fairly well with traditional Ottoman thinking about the people as a “flock” to be managed, and that of the “rightly guided” ruler – if there were objective means to determine who was best suited to rule, why should they not rule? After a particularly bad economic crash, the sultan capitulated and placed a board of scientists and engineers to run the day-to-day workings of government. The scientific oligarchy then decided that the sultan was superfluous to the government, and had him quietly removed, establishing the world's first Technocratic state, which then went on a serious forced-industrialization spree.
At the present day, there exists a Cold War (ITTL known as the Damocles Conflict or War) between the Humanists and the Technocracies. Instead of the economic conflict that characterized the Cold War in OTL, the Damocles War in TTL is characterized by different viewpoints regarding societal progress. The Humanists believe that social progress should be prioritized ahead of technological progress, and vice versa for the Technocrats (in a loose sense: both believe in a rising standard of living, for instance).
The Technates are led by the Ottoman Technate and the Technate of Zhongguo/China, which tends to be rather wackier and more autocratic than the Ottomans. They are run according to the mantra of efficiency and maximum productivity. The government pursues a policy of strengthening the state (inside and outside), the military and the economy. R&D funding is usually higher in terms of % GDP than OTL first-world industrial nations. In schools, practical science and technology is encouraged instead of classics and humanities. Technocratic propaganda is dispensed on a daily basis to the citizens, as well as other nations in an effort to promote Technocratic ideology internationally. However, they are surprisingly mobile societies; as long as you are intelligent and do your job well, you can make it up the ladder with speed.
Technocratic allies tend to be on the authoritarian side: like the US and USSR OTL, they are far from picky in choosing their allies as long as they claim to be “modernizing” and “scientific” in their dictatorial methods.
The Humanist powers, on the other hand, champion tolerance, free thought and sociological advancement. Cultural exportation is enthusiastically promoted, along with the arts and humanities. They still have a strong scientific streak (they have to, to keep up with the Technates), but they consider advancing society primary to technological growth. They enthusiastically promote historical culture to cultivate a sense of national identity. They are capitalist, but with a strong socialist streak; regulation is championed on the basis that the consumer is the most important actor in capitalism. Thus, the governments act to ensure that no corporation ever gets “too big to fail”. Infrastructure and education is heavily invested in to promote growth, and there is also a strong environmentalist streak, with cities featuring a lot of greenery.
The primary Humanist powers are New Sweden, the Ottoman portion of North Antillia, Cartierslande, Thailand, the UK empire, Nippon and Fiore. The Sikh Empire and most European states follow more centrist positions, but are still allied with the Humanists. Russia maintains an informal alliance with the Technocrats.
Owing to Humanist influence, many nations are undergoing cultural revivals, with the UK promoting their Celtic heritage, and the native descendants of the Aztecs in North Antillia putting out some very macabre literature and art (although nobody is advocating the return of human sacrifice).
The Technocratic and Humanist nations tend to be culturally and visually distinct, with rather different ideas on architecture, city planning, even clothing. This extends even to computer hardware. To this day, the Technocratic powers still mostly use mechanical computers, because the user interface is intuitive rather than visual, meaning that one has to be qualified by right of knowledge to operate them. Their use is heavily government regulated, but they have been successfully miniaturized and advanced via development of materials science to make the inner workings lighter, stronger and operate with less friction (the fact that they are immune to EMPs doesn't hurt either). The Humanists utilize the transistor in their computers (invented in the 1930s), which allowed for miniaturization and screen interfaces, supporting the core tenet of Humanism that free interaction and the sharing of various ideas forms the backbone of a prosperous society. Humanist nations have the Internet, while the Technocrats have massive centralized archives of all (government approved) knowledge.
A brief global survey:
New Sweden, including most of OTL Canada but only part of what would be the US, is less populous than our USA, but even richer, a vibrant social democracy dominating an economically unified north America (well, unified aside from the Russians and those wacky Comanches).
Former French South America is, like OTL Latin America, a somewhat backwards and politically troubled area.
India is politically diverse, no single foreign power having managed to call “dibs” the way the Britain did OTL. In the NW, a surviving Sikh empire is an important industrial power, while Portuguese Goa, forced to expand or perish in the face of Ottoman hostility, has become a fair-sized state increasingly independent from the mother country. The rest is divided up by foreign colonial powers into colonies and spheres of influence (increasingly moving towards federation and local rule) and some still-independent local states playing off the Powers against each other.
Japan has done a bit worse: butterflies meant that the unification of warfare-torn Japan under the Tokugawa Shogunate did not occur, and after a brief period of unity under less far-sighted rulers, the country fell apart in feudal warfare again. (On the positive side, this meant that Japan never “gave up the gun”, and foreigners refrained from poking the hornet’s nest). They only recently managed to pull back together (under the title of Nippon) as a result of backing from the Humanist powers, where they have formed a reasonably solid federation, and enthusiastic cultural exporter. One sour note is Hokkaido and Sakhalin: the Japanese settlement of the far north was delayed, the Ainu are more populous (having even briefly created a little tribal “empire” in Sakhalin and the Kurils), and the northern isles have a stormy relationship to Nippon somewhat akin to Ireland's relationship with Great Britain, pre-independence.
Thailand, which conquered and held Burma/Myanmar in the 18th century with the aid of imported European and Ottoman military talent, adapted quickly to European technology. It took the role of 20th century Japan as a great Asiatic economic power and exporter, but with the difference of a lack of militarism and greater self-sufficiency. What they cannot obtain locally, they obtain abroad through a vigorous trading network. They champion Hindu and Buddhist principles of peace and tolerance, having never taken part in a war abroad (although the Burmese and Khmer within the Empire might tell you different).
What OTL would be Indonesia, the Philippines, and Australia underwent something of a colonial “scramble”, with various powers contending for control. Combined with some low-key meddling in the Indian Ocean by the Ottomans, the Europeans worked harder and faster to build up their ports in Indonesia and fortify them against foreign powers, and more European nations than OTL participated. Of course, there were plenty of wars in the process: some colonies got swallowed up; others expanded at their detriment. With this came political and linguistic differentiation and Indonesia was left a network of independent nations each with a different sphere of influence. It can be divided overall, however, into a relatively democratic west dominated by the Humanist powers in an economic and defence union with Thailand as a hub, while the East is dominated by authoritarian dictatorships propped up by the Technocrats. *New Guinea was colonized by Spain, lead by the missionaries, who put a stop to the cannibalism and made good little Catholics out of them, at least in the more accessible regions (they're not doing so well as of late).
Australia is a mixed bag. Victoria, Tasmania and New Zealand have been colonized by the UK, with Victoria, following great economic boosts from the gold rush, becoming another sunny, rich California. The French took the Perth region, while the Dutch took coastal Queensland and New South Wales, establishing a plantation economy there, nowadays somewhat reminiscent of a racist version of Pinochet's Chile. The Portuguese, Spanish and Ottomans took the rest, with the resultant states at varying levels of unpleasantness.
The *Philippines, AKA the Federation of the Sulu Sea, were colonized by several powers, mainly the Portuguese: it is currently in a civil war between pro-Humanist and pro-Technocrat rebels.
China under the Technocrats, its cities even larger, dirtier, and more industrialized than OTL, with omnipresent video surveillance and a fondness for cybernetic modifications, has a seriously cyberpunk dystopia flavor about it, with the elaborate mechanical computing and control mechanisms giving it a touch of steampunk.
South Africa is pretty relaxed on the subject of race, although people of European descent still seem to have a somewhat disproportionate share of the total wealth. It has near-European (the non-nuked bits) standards of living and is a major industrial power: as a result of pressures from its darker-skinned citizens, it has been taking an increasingly anti-colonial attitude towards the European holdings in Africa, something in which it is generally supported by the New Swedes and the Nipponese, a disagreement that some fear risks a serious split in the Humanist block.
The most destabilizing element in Europe is the continued bad blood between France and Spain, which suffered a limited nuclear exchange some decades ago. While France, after a period of military emergency rule, has managed to struggle back to democracy, Spain has turned into a Christian North Korea, the Holy Spanish Republic working busily to purge the state of all corrupting influences and create a pure Catholic state (one with a lot of nukes). The Pyrenees are a heavily fortified border, and “unfortunate incidents” between French and Spanish border guards are all too frequent.
The general trend in this world has been towards federalism, with local governments only serving to implement federal ideas at the local level. There is little established secularism, but the world as a whole is less religious in the sense of worship; many describe themselves as only culturally religious. Religious extremism is looked upon with great suspicion on both sides of the ideological divide: local religious hard-liners tend to go for separation from the ungodly-and-no-doubt-soon-to-be-destroyed-by-a-wrathful-God state rather than political pressure, lacking potential partners in government. In this world, a social safety net is seen as a basic right; indeed, for a nation not to have one in place is seen as inhumane. The question of whether democracy is a necessity for human prosperity, however, remains very much unresolved.