Alt-Onin War - The Mongol Empire

In our world, the Mongol Empire tried twice to conquer Japan in the late 1200's, but failed both times due to a combination of ferocious resistance and ill-timed storms. A century later, the Mongol Empire collapsed into several squabbling successor states. 

In the world of Alt-Onin War, the Mongol Empire remained mostly united under the rule of descendants of Kubilai Khan who were more successful than those of our world. A century later, they made a third attempt and succeeded in conquering Kyushu, Japan's southern major island. The Mongols remain Japan's greatest external threat by Onin 1. 

The Extant Mongol Empire of Onin 1

The Mongol Empire of Alt-Onin had its ups and downs after the death of Kubilai Khan, but it never completely failed. In 1333 the weakening Mongol Empire was revitalized by the ascension of Toghan-Temür Khan, a warlord with connections to the Turco-Mongol Khanates to the west. He restored the cultural connections to the larger Mongol world, and began a deliberate program of de-Sinicizing the Mongols, to restore them to their lost roots. Under Toghan-Temür Khan and his descendants, the Mongols were able to eventually crush the “Red Turban Uprising” in the 1350’s, and the Ming Dynasty never formed. Over the next few decades, the Chagatai Khanate and the Yuan Dynasty formally re-unified. Toghan-Temür Khan's successors were acknowledged as the legitimate rulers of the combined Mongol world, and a loosely unified Second Mongol Empire was re-established, with its capital at a restored Karakorum. Regional sub-capitals were established in Dadu (Beijing) and Samarkand. The Mongol Empire and neighboring Ilkhanate and the Golden Horde to the west remain the dominant powers in Eurasia.

The current ruler is Great Khan Batumonhe Dayan. He is primarily focused on the pacification of South China, and an ongoing invasion of India. Because the Mongol Empire never fell, the Silk Road remained open and active for most of history. The world as a whole is quite different from the one in our actual history. Europe’s great “Age of Exploration” never got started. Europe is a relative backwater divided among numerous squabbling kingdoms, while the Middle East is dominated by the Mamluks of Egypt and countless small sultanates. Little is known of the rest of the world, especially the Western Hemisphere – the existence of a landmass is known to both Chinese and Arab navigators, but nothing is known of the inhabitants of the region. Mongol attentions are occupied by campaigns elsewhere in Asia, leaving Japan relatively safe for the time being. If the reigning Great Khan were not so busy suppressing revolts in southern China, they would probably be at war even now.

Mongol Invasion and Occupation of Japan

The Mongol invasions of 1274 and 1281 both failed, due in part to the appearance of a typhoon at an opportune time. The chaos of this period contributed to the fall of the Kamakura Shogunate, and its replacement by the current Ashikaga Shogunate. In Alt-Onin, a third attempt in 1388 proved to be successful, as no storm appeared to save Japan. The samurai were able to slow the pace of Mongol conquest, but the learning curve was steep, and the human cost was immense. By 1391, little of Kyushu remained in Japanese hands, though the repeated attempts to land Mongol troops on Honshu invariably ended in defeat at the hands of fanatical samurai defenders. The Japanese were able to retain control of Bungo Province and the region around the city of Kagoshima for several years. 

In 1394, the Shimazu and Otomo clans retreated to lands in the Kanto, granted by the Oda to the fleeing Emperor Go-Kameyama. This triggered two decades of small wars in the provinces around Edo as the Kyushu clans displaced local clans which opposed the newly established Eastern Court. The Ashikaga Shogunate in Kyoto managed to establish a tenuous peace with the Mongol Empire in the 1390’s, which now recognizes Japan as a “tributary state”. The Ashikaga, in turn, made pretenses of being equals to the Mongol Empire, a polite fiction that fooled no one but nevertheless kept the peace for a time. This peace arrangement is largely rejected by the Eastern Court, which now regards the Ashikaga as traitors. 

The Mongols have established themselves as the lords of Kyushu and integrated it into their larger empire. Kyushu and the former Kingdom of Ryukyu are ruled together as a single province called Zuun Arlud, the "Eastern Islands". 

The Mongols have established a permanent settlement at Aral-Khorgod (once called Fukuoka), which is home to a large foreign population of Koreans, Chinese, and others from more distant parts of the empire.  The remainder of Kyushu is dotted with small villages along the coasts and rivers, while the majority of the island has reverted to wilderness. The coasts are patrolled by Mongol forces on ships crewed by Koreans. 

In the current era, Japan is a relatively insignificant part of the Mongol Empire, a thorn in its side not considered enough of a problem to crush just yet.  Two years ago the Mongols attacked Nagato and Suo provinces in retaliation for the interference of the Ouchi Clan. The Mongols have razed most settlements in the two provinces, but these areas remain hostile to Mongol rule thanks to a permanent guerilla resistance. This new aggression by the Mongols has re-opened the controversy around the "Ashikaga Peace", stirring up disputes across Japan. 

The constant warfare against the Mongols and their relatively advanced technology has spurred the development of Japanese military technology, so that the armor, weapons, and organizations of the 1460's resemble those of the historical 1500's - more functional body armor, and more formally organized armies. Gunpowder weapons are no more advanced than they were historically and are relatively uncommon.