The real threat comes from the
Mongol invasion of Sakhalin.
The Jurchens revolt in 1343 and by 1348 declare independence as the Later Jin.
Turns out I didn't read my sources clearly enough. There was a Jurchen revolt in 1343, and some Jurchen clans claimed the title of Jin successors in 1348, but it wasn't a Manchuria-wide rebellion where the Yuan lost complete control. The Yuan retained control over Manchuria (as "Liaoyang Province," which I'll use for Chinese (遼陽) and Korean (요양/
Yoyang) administrative units in the future and DE instead of Nurgan, which will still remain as the Jurchen name) until the Ming invaded in 1387, long after the Yuan had collapsed in China proper. That helps me on the "Yuan don't completely collapse but remain in Northern China with help from the Timurids and the rest of the Mongol Empire" front, and I no longer have to move up Goryeo's northern expansion to the 14th century. Since the Ming are in no position to project power in Northeast Asia for a long time, Goryeo has all the time it needs to slowly expand against the Yuan remnants and Jurchen tribes. That also lets me preserve parts of the "Big Manchu" blob by having it be part of the Yuan remnants. So I could have the Mongol puppet shogunate survive a bit longer, until it's isolated by Goryeo conquering mainland Manchuria and Sakhalin, after which it falls apart and Goryeo gets an opportunity to invade from the north.
Here's a reworked timeline from the 13th century up to the final conquest of Japan, this time incorporating much of the original game’s progression. The years are subject to change of course.
1250s: Goryeo’s Ch’oe clan, which had dominated the military regime for generations, continues to have competent leaders and is not overthrown by other generals. The military dictatorship evolves from a coalition of generals into a hereditary office under the Ch’oe.
1270s-1280s: Song Dynasty falls but Goryeo and Dai Viet do not. Kublai Khan decides to cut his losses for now and eliminate Japan through Sakhalin and Kyushu, then invade Goryeo from the south. The 1274 invasion of Japan doesn’t happen due to no Goryeo to launch the ships from, but 1281 is slightly stronger and draws on more troops and ships from the recently conquered Song. They successfully establish a foothold in northern Kyushu at Tsushima and then Hakata. The provincial capital at Dazaifu falls soon afterward, after the Yuan defeat a massive coalition of local lords on land and a storm sinks thousands of Japanese reinforcements and their noble commanders sailing to retake Hataka. Most of Kyushu falls into Yuan hands by the end of the decade, but resistance continues in certain mountainous regions and fortified castles (some of which, ironically, were built with the help of Baekje centuries ago). More reinforcements come in from China, particularly ships. This sets off alarms within the Ch’oe, which concludes Goryeo is the next target immediately orders a naval buildup. It takes a couple years, during which the Yuan finish subjugating Manchuria as Liaoyang Province, resettle Chinese and Koreans in the frontier regions, and then invade the Ainu in Sakhalin and Hokkaido. The major Ainu chiefs largely submit by the end of the decade (about 20 years earlier than OTL), so the Yuan invade northern Honshu with a large army of Mongols, Chinese, and Jurchens, taking advantage of rebellions from Buddhist sects and rival clans fighting each other over Ainu trading privileges. They advance far south, where they meet massive resistance from the Kamakura shogunate and the clans in the area. But the shogunate itself faces rebellions from clans opposed to the Hojo. The Yuan restore the destroyed Fujiwara city of Hiraizumi as their capital until they take Kamakura.
1290s: Finishing its militarization, Goryeo attacks the Mongol fleet at Tsushima. The surviving ships, mostly captured Song riverboats, are subsequently destroyed in a storm, which the Japanese interpret as Goryeo being divinely favored. Goryeo then invades Hakata and captures Dazaifu. It forms alliances with local clans to reinforce its armies as they destroy the Yuan forces in the rest of Kyushu. Meanwhile, the Yuan forces in the north sack Kamakura, leading to the collapse of the Hojo clan and the shogunate. A new pro-Yuan clan is appointed as
darughachi and shogunal regents in Kamakura. Japan between Kyushu and Kamakura falls into chaos as clans fight each other over who should the rightful shogunal regent or just shogun outright. Goryeo props up its own clan as regent. Kyoto falls, and with it the Japanese imperial house falls into Yuan hands. The Yuan install their preferred imperial prince on the throne and a second prince as a shogun, while other princes escape to Kyushu to seek the backing of Goryeo, whom they see as the only power strong enough to defeat the Yuan. The remaining clans of western Honshu submit to the Yuan shogunate soon after, but Shikoku remains independent of both Goryeo and the Yuan. By 1300, the two sides have their own puppet emperors, shoguns, and shogun regents. On the Mongol side, while their puppet emperors and shoguns remain drawn from the northern court, the regents eventually come from a Borjigin cadet branch which also intermarries with the northern court. On the Goryeo side, the southern court contributes the emperors, but the shoguns and regents are drawn from not only the southern court but also pro-Goryeo clans, the Ch’oe clan, and even the imperial house of Goryeo.
1300s-1340s: The Yuan consolidate their hold over Honshu, though the clans of western Honshu, funded by both Goryeo and the independent clans of Shikoku, submit in name only and remain effectively independent. Many Jurchens, Chinese, Mongols, and Manchurian Koreans are settled in northern Japan as shock troops, while others are settled in Sakhalin and Ainu Mosir. The roots of Japanese Christianity are found here when Church of the East bishops from Central Asia and Roman Orthodox priests from the Reich (arriving after Roman-Mongol relations are normalized) establish churches in Kamakura. Goryeo remains in a constant state of war with the Yuan. Its navy raids cities along the northern Japanese coast to preemptively destroy any fleets being assembled to invade Goryeo. Its army wages a war of attrition in Manchuria against the Yuan, which is still fighting the Tran in the south among other enemies.
1340s-1360s: The Yuan Dynasty collapses in China. Despite some Jurchen rebellions (which Goryeo uses to its advantage by either conquering the rebels first or swaying them to its side for military protection), the Yuan stay in power in the north and Manchuria with reinforcements from the Timurids and Japan. The Yuan shogunate also remains in power, heavily relying on the north court for legitimacy, but many Japanese clans grumble when their troops and sons are sent off to die as reinforcements for the mainland Yuan against the Ming. Still, Japan’s urbanization and relative prosperity compared to the chaos in Mongolia and the rural wilderness of Manchuria keeps the Yuan afloat. In the coming decades, as Beijing and northern China become buffer regions and the site of many battles with the Ming, the Yuan become increasingly centered on and ruling from Kamakura, relying heavily on Japanese and Jurchen soldiers for its armies.
1360s-1420s: Goryeo gradually expands in Manchuria, chipping away at Yuan power as part of an alliance with the Ming, which recognize Goryeo's Balhae and Goguryeo claims to the region. The Yuan meanwhile march north to subjugate the Siberian tribes and add them to their army. Mass resettlements of Chinese, Korean, and Jurchen communities in Manchuria to Outer Manchuria and Siberia take place, both to remove them from the Ming/Goryeo border regions and to "civilize" the frontier.
1450s: The Ashikaga clan seizes power in Kamakura and proclaims a new shogunate free of both Goryeo and the Yuan, but their rule crumbles as the western clans rise up in full rebellion and civil war breaks out. Yuan rule is pushed back to the provinces north of Kamakura. The capital is relocated back to Hiraizumi, where the first recorded ancestor of the Aisin Gioro clan, Möngke Temür, appears as a talented warrior in service to the Yuan. The Mongol ruling class finds itself increasingly torn between its Jurchen, Japanese, and Chinese subjects.
Early 1500s: Fusang gold and silver begins arriving as contact is established and trade routes set up, creating an economic boom in the Ming, Tran, and Goryeo. Roman traders bring with them Roman Orthodox Christianity, now with another 200 years of theological innovations. Japan remains fought over by Goryeo, the Yuan, and the independent clans, of which the Shiba are a rising power and the Ashikaga are on the decline.
Mid-1500s: The gap between the Borjigins of Mongolia and Japan widens even further. The former was propped up by the Timurids and the Onggirat clan, but when the former is destroyed by India and the latter suffers heavy defeats to the Ming, their power base weakens, exposing northern China to Ming invasion. On the other hand, the descendants of Möngke Temür gradually gain power in the Hiraizumi court and secure the allegiance of the Jurchen tribes on the mainland.
Late 1500s-1600: The Ming decisively crush the Yuan in northern China and then Mongolia proper, leaving the Borjigins of Japan the last of the imperial Yuan. The Yuan initially remain in northern Japan, Hokkaido, and Sakhalin, but the current descendant of Möngke Temür, Nurhaci, takes offense to the Borjigins for killing his father in 1583, among other policies favoring the Japanese over Jurchens. Central Japan is fought over by the Ashikaga, Shiba, and a few other clans, and Kyushu, Shikoku, and the western edge of Honshu are firmly under Goryeo's control. Goryeo conducts its ill-fated invasion of Ryukyu shortly after completing the conquest of Shikoku with the defeat of Tsuruhime, and the Ryukyuan sack of Kaesong in retaliation deters it from further Japanese expansion for a while. The Shiba daimyo converts to Roman Orthodoxy to get priority access to Roman weapons.
1600-1620: Nurhaci deposes the Borjigins, dissolves the Yuan shogunate, and takes over the remaining Yuan territories in Manchuria, Siberia, and Japan (and causing chaos in the former two that the Ming exploit). He claims the surname of Aisin Gioro for his family and proclaims the Later Jin Dynasty. A brilliant military mind, his motivated troops destroy the Ashikaga and capture Kamakura. In response to the dissolution of the shogunate, the northern court relocates to the southern court and is absorbed into it, granting the Goryeo shogunate more legitimacy. Speaking of which, the Goryeo shogunate and the Goryeo military regime have become one by now as the Ch’oe clan formalizes its hereditary military dictatorship and, borrowing from Japan, begins prioritizing the use of the title
janggun. The combined northern and southern court eventually grant the title of shogun upon the current Ch’oe
janggun, merging the titles into one. The Ch’oe clan declares that the emperor of Japan has submitted to the emperor of Goryeo. Goryeo continues its economic boom and sets up trade outposts in the far northeast of Siberia and on the Pacific Northwest coast, hoping to set up its own trade routes without going through Ryukyu or the Ming/Tran-dominated Qiandao Islands.
1620s-1640s: The untimely death of Nurhaci interrupts his plans to conquer the rest of Japan to use as a power base to push the Ming out of Manchuria. His son Hong Taiji takes over for him but immediately faces rebellions from the Japanese clans under his rule, Borjigin loyalists, the Ainu, and fringe Buddhist sects. The Shiba clan seizes on the opportunity to strike and launches a full invasion, starting with taking back Kamakura to boost their legitimacy. In 1648, they take Hiraizumi and drive the Later Jin out of Honshu. The Later Jin completely collapse at this point as the Ming and Goryeo (under a
janggun favoring Manchurian expansion over Japanese expansion) carve up Manchuria, their armies fueled by Fusang gold and silver.
1660s: The collapse of Later Jin is complete with the conquest of the last Jurchen lands in Manchuria by Goryeo in 1660. All that are left are scattered clans in Siberia and Borjigin loyalists/Aisin Gioro remnants fighting Ainu lords in Hokkaido. The rest of the decade sees these clans turning on each other in an attempt to claim an imperial title, while Goryeo, the Ming, and Fusang gradually enter Siberia to finish the job.
1670s: Goryeo invades and conquers Ainu Mosir while its Ainu, Japanese, Jurchen, and Mongol clans are still fighting each other. The ascension of a new janggun favoring Japanese expansion sees Hokkaido used, much like the Yuan did almost 400 years earlier, as a staging ground to invade Japan from the north. In Siberia, the Yukaghir people (the “Khodynt” tag) and “Kamchadals” (since they were descendants of natives and Ainu who assimilated with Russians, I’ll have these ones be similar but they assimilated with Jurchens, Koreans, Fusangren, and Yavdians) break free of Jurchen rule with Fusang’s help, while Fusang expands its trade outposts in Siberia. By the end of the decade, Fusang has brought much of far eastern Siberia under its control. Goryeo begins suffering massive inflation and enters a period of economic crisis, forcing the
janggun to put his invasion plans on hold.
1696: The last Jurchen clans are finally subjugated by the Ming, Fusang, and to a lesser extent Yavdi.
1699-early 1700s: Obsessed with conquering Japan, the
janggun agrees to a Ming offer to supply the cash and troops in exchange for more trade privileges and “advisors” in the Goryeo imperial court. The invasion commences a year later, and by 1701 Goryeo has taken northern Japan. The next ten years become a slog as the Shiba desperately throw everything they have against the invaders, but the combined Sino-Korean alliance has limitless men, a massive treasury, and the most advanced weapons in Asia. The Reich is unable to assist due to the distance, but it sends ambassadors—a Church representative contacting the Metropolitans of Kamakura, Nanjing, and Kaesong—in an attempt to negotiate a ceasefire. By 1713, the Shiba have been reduced to the area around Kyoto, which is initially left alone provided the Shiba acknowledge Goryeo’s superiority and claims to the rest of Japan. The modern border gradually starts developing due to differences in how the older conquests of southern Japan are administered (Koreanized, with some allied clans remaining) compared to the newer northern Japan conquests (a mix of Christians, Jurchens, Japanese, Mongols, Ainu, Koreans, and others).
1728: Increasing intermarriage between the Ming and Goryeo imperial houses results in the military regime losing power and legitimacy as it now comes from the Ming via the Goryeo imperial family. Those who could speak Chinese, were well educated in Confucian classics, or had access to the Ming court or the Goryeo imperial family gained greater influence, while the
janggun was discredited due to his costly war in Japan and the political sacrifices needed to achieve it. The Ch’oe clan is subsequently overthrown when the Goryeo emperor orders their political and military authority revoked. The Shiba clan attempts to rebel at this time, hoping to take advantage of the political instability, but their rebellion is crushed and Kyoto brought under direct Goryeo rule. The emperor of Japan is forced to acknowledge the suzerainty of the emperor of Goryeo via the
janggun of the Ch’oe clan, which remains in power as shoguns of Japan despite losing power in Korea. From here on, the
janggun transitions into an office akin to a colonial governor. Due to financial difficulties and the recent regime change, Goryeo is forced to let the Ming co-rule Japan, and the colonial administration of the
janggun is filled with Chinese bureaucrats aside from in Kyushu, Shikoku, and Hokkaido/Sakhalin, which are considered full provinces of Goryeo. Goryeo is also forced to sell its Siberian and Pacific Northwest colonies to the Ming and Fusang, ending its colonial aspirations. For the next few centuries, it focuses on holding what it already has while trying to claw back its independence.
