1400s: Plague, War, Turmoil, and the start of the European Renaissance
The 1400s started out with things going pretty well in most of the Old World, and chaos in the New World. Often, at first contact, native populations melted away seemingly overnight, and the colonizers gained new territory. Japan gained much land and riches, but was increasingly at odds with China and Korea. The Chinese tried to call a conference with the leaders of Japan to carve up the New World into separate spheres of influence, but the Japanese felt that they were in a good position and declined the offer. Japan, after all, had a large head start in the New World. Because of Japan's unwillingness to cooperate, China declared war in 1411.
Sino-Japanese Colonial War
China based some troops on the northern shore of the island of Taiwan (a mostly tribal island at this point) and Jeju Island (of Korea, by treaty), as well as sending ships to the New World via Hawaii. The stated reason for the invasion was the disrespect of China, including the unwillingness to curb piracy in Chinese waters and (the main reason) an unwillingness to settle border disputes in Yodderick. This war also came soon after the Chinese and Japanese realized that South Yodderick (South America) was another huge continent that could be exploited. This war, especially overseas, was a good test for the new Chinese-designed warships. Chinese cannons were prominently used at sea on these ships. The first attack was on Kyushu Island, on a major trading port. The Chinese were not bent on taking Japanese land, but rather on proving the point that China should not be crossed. Thus, the Chinese set fire to settlements instead of taking them standing. This tactic was especially prominent in Yodderick, as the first incarnations of Yamami and Heino (each with more than 1000 people) were almost completely burned to the ground, with the populace scattering into the outlying areas. The most disastrous event is known as the "Burning of Naniwa", and was a huge Chinese assault on central Osaka. However, for all of this, the Chinese couldn't make it far on land in any Japanese place. A new breed of highly skilled samurai cut down the Chinese armies that dared to get beyond sight of the sea. Kyoto remained completely unscathed. In the end, the Japanese continued to refuse to recognize China as a greater power, and the Chinese council voted to halt the war, as it was turning out to be more difficult than imagined, and they believed that the troops would be better used elsewhere. Each side claimed victory, and the end of the war saw the situation stay essentially the same as before the war, only China recognized Japan as more of an equal.
The Great Plague
For the past 100 years, Asians were only used to seeing plagues hit the native people of the New World. These plagues were of smallpox and such, and were less lethal to Old Worlders. While the Asian colonizers often tried to fight smallpox and help the native people (successfully teaching them new techniques like rubbing smallpox pus in wounds while healthy so as to increase resistance later), what was a great problem for the natives of Yodderick was a more trivial problem, and occasionally an opportunity, for the Asian powers. This way of thinking came to an end when in 1432, a great plague, often called "The Great Plague" swept Asia, Africa, and Europe. It is still not known exactly where the plague spread from, but most accounts have it hailing from Central Asia, near the former Kipchak. China was again on the move, conquering the west, and attacking the outskirts of Moscow and Novgorod, as well as the Crimea when the problems arose. From within the Chinese army, there arose a horrible disease that killed half of them. This disease picked up in Russian areas and spread toward Europe. Sri Vijaya, a major power doing business with many European and Asian cities caught the disease and helped to spread it (but - in a way - thankfully, most traders died before ever reaching the main islands). Soon, much of the known world was sick, and deaths piled up, eventually taking away a good chunk of the population of many countries. Colonies, if they hadn't been burned in the Sino-Japanese Colonial War, shriveled up and stayed barren for decades. Many of Sri Vijaya's African possessions again became uninhabited.
The plague burned out after a few years, but things were never the same. From that point on, disease was on the mind of almost everyone, and people looked for ways to make things cleaner. People in Europe had varying methods of dealing with the horror. Some became more spiritual, and more religious sects within Christianity appeared. Others gave up religion altogether. In fact, disbelief in God climbed to new heights. During the plague, Japan had sealed off its ports and had those sick people expected of being infected by the plague executed. Because of this, it came away stronger than most other countries. Most Europeans accused the outsiders (i.e. Asian nations) of having started the plague and many kings told their armies to kill any foreigners on sight. Sri Vijaya suffered greatly, as its main function - trading - was severely disrupted for years. At the end of the plague, Sri Vijaya's territory was actually smaller than it had been 100 years prior. Several states broke away from within the archipelago also. Some Dayak (Bornean) tribal communities rebelled. There was a fear that the country might not last intact and instead would become a collection of small kingdoms. Also during the plague, the last vestiges of ethnic Chinese leadership in Persia disappeared.
Japan was the first major nation to recover. Having not suffered like the other nations, it was less reticent to continue its exploration. Within two decades after the Great Plague ended, Japan's colonies had regained their previous (pre-War) sizes. In 1464, Japanese explorers rounded the Great Southern Strait (大南海峡 [Dai Minami Kaikyou], Strait of Magellan). Then, in 1473, another voyage was the first to make it around the world by rounding the Southern Strait, crossing the Atlantic to Europe, going around Africa, and passing through Sri Vijayan waters.
Indian Nations prosper
Another region not as hard hit by the plague was India. Taking up much of the north of the subcontinent was the Delhi Raj, a kingdom made up of a conglomeration of smaller statelets. Taking up the south was the Vijayanagar kingdom. Hindus made up the majority of the population in both kingdoms, although Jainism, Buddhism, and other faiths also were able to flourish.
As a populous nation, China's situation during the Great Plague was unique. On the one hand, the proximity of people to each other caused outbreaks nearly everywhere in the northeastern plain, which was the main power base of Beijing. On the other hand, though, China's large population meant that even after the plague, it still had a large workforce who could soon rebuild. China also developed various medicines and medical procedures during and after the plague, which helped to prevent disease. Indeed, medicine experienced a coming of age in the decades including and following the plague. Strict cleanliness laws were passed, and this aided China in the long run. At the end of the plague, China was in an even stronger position vis-a-vis Europe than even before the plague, as it had somehow come through the ordeal with less chaos.
The New Conquests
By the end of the 15th century, China was again at Europe's door, and was able to make some eastern European states into tributary states. This was accomplished by its old method of extensively training armies, especially used to huge climatic hardships (such as encountered in north Asia) and sending them across the desolate tundra and taiga almost unimpeded until they encountered Eastern European population centers. In 1489, China had conquered the Russian states, Lithuania, Poland, Saami areas, and the Crimea. Only in Russia and the Crimea did China gain direct control of, but the others, as tributary states, became China's pawns so as not to risk further attacks. China treated its conquered people relatively amicably, letting them continue to live as before, speaking their own languages and worshipping their own (mostly Christian) God, and few Chinese settled in these lands. But a class system developed. These conquests established an idea of Oriental superiority over Europeans. This idea was not codified into law, or even often expressed in public, but just by practice, it became an entrenched idea. (The Renaissance (see below), in part, came to be perceived as a reassertion of European pride, mostly erased in Western Europe since the fall of Rome.)
Europe Post Plague
Europe was a mixed bag post plague. In general, Europe became more religiously diverse and more xenophobic. Catholicism, followed by the vast majority of Christians in Western Europe, suffered a huge blow. During the plague, people appealed to the church to do something. Praying didn't seem to help. The Pope, a single representative of the religion, was blamed in part for the misfortunes of the masses. It was widely learned that the Pope lead a royal life of luxury, even through the plague. Those that continued to stand by the Pope during these times of woe, blaming sinners for bringing the plague on themselves, were shocked when the Pope also caught the plague and soon died. The following Pope was ruthless toward anyone who appeared to be sick, and mostly sealed himself off from the outside world during his tenure. Because of this, faith in the Pope being a representative of God on Earth began to wane. Out of formerly Catholic populations came various sorts. The majority became more skeptical and less religious. Many others converted to Catharism, as it seemed to be less corrupt. There was no hierarchy the like of which was in Catholicism, and Cathar areas were also recognized to be more resistant to the plague (perhaps because people often worshipped at homes in their own neighborhoods in smaller numbers rather than going to a large church that could hold many people - and transmit a disease more quickly, or because of the Cathar reliance on action over prayers). A minority got involved in fringe cults. The great trading routes prior to the plague had also transferred many ideas to Europe. The Byzantine Empire had knowledge that the rest of Europe had forgotten, and this got disseminated in the 14th and early 15th centuries. Especially after rediscovering Europe's seemingly glorious past (which had been extinguished upward of 1000 years prior) many Europeans felt that Europe had decayed since then. They looked at architectural styles, philosophy, and culture from a period before Christ, Bishops, Popes, and the East Asian nations and found that all of these recent importations hadn't helped them much. Even diehard Christians recognized the profound achievements of prior generations. Modern-day Greece (the Byzantine Empire) and Rome (the Italian states) gained more recognition and served as sources of inspiration. Europe was starting on a new path, and Greco-Roman influences sprung up everywhere and in everything.
Also owing to the influx of these ideas, Milan, Florence, and Genoa broke away from the Holy Roman Empire (Venice was already independent), as the Empire was dominated by ethnic Germans, and were thought of as descendants of the Germanic tribes that overthrew Rome (with a legacy continued on by Romance language speakers such as those found in the northern Italian states). Outside rule was no longer desired, and these areas successfully gained independence. Some other areas (mostly duchies that no longer wanted to even pretend that a higher authority existed) broke off. The Holy Roman Empire, a weak nation made up of widely varying parts could not do much to stop this breakup. The Papal States, under the Pope, tried to reunite the Holy Roman Empire through diplomacy, but this failed. It is also worth noting that for the time being, the eastern Slavic parts of the empire (Bohemia, Silesia, and Moravia) stayed loyal parts of the empire, as they feared a Chinese incursion from the east.
The Middle East's New Paradigm
It was during the plague that the Byzantine Empire (which I may also refer to as Byzantia) lost Arabia for good. Rebellions sprouted, and it became apparent that the worth of Arab lands was substantially less than the cost of continuing to occupy them. Besides, the Muslim threat was over. Arabia had been Christianized over the preceding 100+ years. Still, the type of Christianity practiced in the Middle East was changing. Byzantia had hoped for an Orthodox population, but it turned out that some Orthodox ideas mixed with those of the Western (Catholic) crusaders who stayed in the conquered territories. And added to that was a dose of radicalism and nomadic backwardness. Pope-worship gave way to the worship of "holy men", "soothsayers", "prophets", and others who distorted what the Byzantines believed was true Christianity. Over time, these small sects would either die off or grow and combine with others to create a new brand of Christianity in the Middle East. However, the Byzantine Empire held on to Egypt and the Levant, and went as far as widening the "Red Sea to Nile Canal" in an attempt to bring back boat traffic to previous levels. At first, because of European xenophobia, boat traffic stayed low, but in succeeding centuries, it became busier and busier.
Sri Vijaya Tries for a Comeback
Over the latter half of the 15th century, Sri Vijaya tried hard to re-establish its colonies over its previous African trade route. Although few powers could stand in its way (as Africa had few kingdoms powerful enough to repel the Malays from their coastal outposts), Sri Vijaya also realized that its main prize was not Africa itself (where wild animals, malaria, and other other dangers abounded, and which lacked any trading partner that could significantly enrich Sri Vijaya) but with European trade that the African trade route previously secured. But with increasing peace in the Middle East and the reopening of the Egyptian canal, and with the more wary Europeans, Sri Vijaya started to feel that it was losing out to its competitors. But during the last few decades of the century, Sri Vijaya set out on exploring southern Africa in depth. (This would eventually lead to them discovering diamonds in the early 1500s.)