Note: This should by no means be taken as a comprehensive timeline. It is, rather, an outline intended to hit a few key points of technological development and historical alteration. All named individuals are actual historical figures.
8th C: Tang dynasty The printing press has been invented and movable type spreads when an influential scholar from the court comes across Bi Sheng a lot sooner. Trade with Silla (Korea) brings in the innovation of metal type, possibly invented by an ancestor of Choe Yun-ui. The spread of printing is driven by scholars at first. Increased communication encourages settling on consistent terms and explaining one’s logic, which leads to a firmer theoretical grounding for advances to build on. This lays the groundwork for developing large-scale production which can be duplicated to the same end in many places. I posit that this will be sufficient to counterweight any philosophical convictions that logic is insufficient to comprehend/describe nature (a conviction which may lead to quantum physics really early, though).
10th-13th C: Song dynasty A period of growing meritocracy and bureaucracy. The need of the bureaucracy to oversee and communicate with an expanding population drives the further spread of printing and literacy, and advances in the sciences are also printed and disseminated more widely. Rural centers of government away from the capital distribute effort and promote competition; I posit an intensification of the general trend toward reliance on local gentry to govern the growing population. Military and naval development are driven forward by pressure from the Mongols and, later, the Jin dynasty in north.
13th-14th C: Yuan dynasty The Mongol dynasty during the Mongol Empire. China is not as comprehensively smashed as some other nations, but it causes a hiatus in development, as it does across the continent.
14th-17th C: Ming dynasty This is a period of stability and growth. The Ming gather a considerable standing army and pursue great construction projects: the Grand Canal, the Great Wall, the Forbidden City. An agricultural surplus leads to an export economy and increased wealth. The merchant class begins to field a significant number of governmental candidates. I posit that this prosperity also fuels a technology explosion as more people are free to engage in it over and above subsistence. In the 16th C China enters global trade. The Little Ice Age at end of the period, however, brings an agricultural crash, wrecks the economy and leads to trade interruptions and great unrest.
17th-19th C: Shun dynasty I posit the Manchu invasion and the Qing dynasty actually do not take place. Li Zicheng’s peasant rebellion succeeds and his forces reach General Wu Sangui before Wu lets the Manchu in past the Great Wall as allies. The Manchu coalesce into a separate nation, allied with the Mongols. This dynasty is, rather, the Shun dynasty, a period of some upheaval resulting in some decentralization of power. Land-ownership is given to the peasantry, though the government keeps a significant standing army to maintain control. The reform of exam standards, exchange rates and corrupt officials still happens. The Macartney trade embassy from Britain happens a lot earlier and global trade is resumed. There is a good deal of technology development as the tech race gets going, spurred by constant wars all over the world and the exchange of ideas created by trade. Technology and art trade staves off economic stagnation. There is no Taiping Rebellion. There are no Opium Wars because trade was never closed off; in addition, everyone is already too well armed on both sides and military confrontations, unless instantly decisive, are considerably more dangerous and costly.
10-14th C: Goreyo dynasty This is an era of unification and governmental reform. Increased civil freedoms support advances in scholarship and technology, and literacy spreads. There is considerable exchange with the Song dynasty. By mid period, two Khitan invasions and the depredations of Japanese pirates drives development of weapons, Choe Mu-seon’s ship-based weapons in particular. During the end of this period, the government is considerably weakened in the aftermath of war with the Mongols and under the control of the Yuan dynasty.
14th-19th C: Joseon dynasty. After considerable dynastic struggle, the new and more centralized government under Sejong the Great supports advances in science and the arts. By the 16th C central support is less and internal division worsened, but trade with Ming keeps greater momentum going. Weapons development is sufficient to beat off Toyotomi’s invasion with considerably lower losses, and, without the threat of Manchurian invasion and the Qing dynasty, Korea does not isolate itself nearly as much. Trade and development continue while the late Joseon rulers turn again to unification and reform.
10th-12th C: Heian period This period was the height of import and elaboration on Chinese culture, and the start of serious divergence into domestic innovations. The lapse in diplomatic relations due to the Five Dynasties Ten Kingdoms period after Tang’s fall spurs local development. There is still some trade, though, and when traders return with books of arts and science scholarship it leads the government to revive relations and expand trade. The printing press is adapted to local syllabary to distribute literature, and the new availability of printed materials leads to increased literacy.
12th-14th C: Kamakura period The first bakufu, or shogunate. Mongol invasions during 13th C introduce pressure to increase naval and technological development.
14th-16th: Muromachi period 1467-1600 is Sengoku, the Warring States period, and during this time firearms are imported from China and Korea. The first European trade contact is still the Portuguese, in 1543, which introduces some European and Ottoman variations on technology. Artisans experimenting with both kinds of imports are the start of what will become a separate class. Nobunaga, Toyotomi and Ieyasu follow in order to bring an end to the civil conflict. Toyotomi’s attempts to invade the mainland are turned back with some fairly advanced weapons; Ieyasu turns this to his own purposes by emphasizing the threat of outsiders to help unify the nation.
17th-19th C: Tokugawa period Codification of the class system includes technological artisans, who themselves include some unaffiliated samurai left after the Tokugawa consolidation, preferring to be weapons artisans rather than give up weaponry entirely to become farmers. The Shimabara rebellion still results in limiting Western trade; this requires more open trade with China, despite the deep distrust in which the Tokugawa bakufu holds the rather populist Shun dynasty. Trade passes through Dejima island, so that imported books and products can be vetted for political suitability. The distrust cultivated by the government drives the development of land-to-sea weapons in particular.
19th C: Meiji period A military-trade envoy from the Tlaxcalteca-Spanish state of Nahua (Mexico) is sunk by the defensive emplacements. In the wake of this, the Anasazi (Pueblo) nation sends a pure trade delegation instead, and examples of the products that the technology revolution in the Americas have produced leads the bakufu to re-open the country to trade. This change of policy is taken as an excuse by internal factions, and the simmering tensions of the Tokugawa period explode into the Meiji revolution. Without the panic caused by unequal weapons and treaties, however, there is no national shame, less psychotic nationalism, and less of a headlong drive to emulate Europe philosophically and politically. Japan loses its impetus to become an imperialist power and never invades or occupies Korea or Manchuria.