# 【67-10】クビライあきらめない！日本侵攻の果てに待つ鎌倉幕府の変化【COTEN RADIO モンゴル帝国襲来編10】 - Show: 歴史を面白く学ぶコテンラジオ （COTEN RADIO） - Published: 2026-10-19 - Canonical: https://podc.club/en/episode/1450522865_a266c34e057c.html - Audio: https://anchor.fm/s/8c2088c/podcast/play/125576414/https%3A%2F%2Fd3ctxlq1ktw2nl.cloudfront.net%2Fstaging%2F2026-8-11%2Feafc8677-987f-cf02-a29f-5977993ef1ef.mp3 - Source: Edited from a machine transcript of the first 30 minutes of the episode. Not an official summary. Even after Japan repelled the second Mongol invasion at the Battle of Kōan in 1281, Kublai Khan refused to give up — ordering the construction of 3,000 warships and repeatedly planning new expeditions. Then the man who had led Japan's defense, Regent Hōjō Tokimune, died suddenly at 34, leaving a 14-year-old heir and opening the door for Adachi Yasumori to push through sweeping political reforms known as the Kōan Tokusei Decree. This episode traces Kublai's obsession, the transformation of the Kamakura shogunate, and the ideological roots of the concept of 'tokusei' (virtuous governance). ## What this episode answers ### Did Kublai completely give up on invading Japan after the Battle of Kōan? No — Kublai never gave up, continuing to order shipbuilding, plan new expeditions, and send envoys to Japan right through 1293, when the last envoy was detained in Kamakura and died without ever exchanging a single word with the Japanese. ### Why did Mongol forces repeatedly fail against Japan and in Southeast Asia? Geography was decisive: the sea blocked Mongol cavalry tactics against Japan, while dense jungle neutralized them in Southeast Asia, and epidemic disease spread rapidly in the humid climate, severely depleting their forces. ### What impact did Hōjō Tokimune's death have on the Kamakura shogunate? Tokimune died suddenly at 34 in 1284, leaving his 14-year-old son Sadatoki as successor; unrest emerged within the Hōjō clan, and it is said the situation would have been extremely dangerous had the Mongols attacked during this period of upheaval. ### What was the Kōan Tokusei Decree, and who led it? Adachi Yasumori (安達泰盛) led the reform, which comprised over 90 articles — including Sadatoki's vow of frugality, establishment of the shogun's direct landholdings, enrollment of non-gokenin fighters from the Battle of Kōan into the gokenin class, a crackdown on lawless elements, tax reductions, and the return of shrine and temple lands. ### What ideological traditions underpin the concept of 'tokusei'? The concept draws on two Confucian ideas: Dong Zhongshu's (董仲舒) Heaven-and-humanity correspondence theory (disasters reflect the ruler's lack of virtue) and Mencius's mandate revolution theory (the people may replace an unvirtuous dynasty) — though in Japan the revolutionary clause was gutted, leaving only frugality, good governance, and restoration of shrine lands. ## Article ## Kublai's Obsession — Invasion Plans That Outlasted the Battle of Kōan After Japan repelled the second Mongol invasion at the Battle of Kōan in 1281, the Kamakura shogunate itself briefly considered a counter-offensive — mobilizing gokenin from Chikuzen, Hizen, and Bungo provinces under commanders from the Ōtomo clan to pursue the retreating Mongol forces. The plan never materialized, and an order to gather some 56 akutō (outlaw strongmen who seized land by force) in Kyushu also came to nothing. On the Mongol side, retreating soldiers reported that the storm had beaten them, and Kublai refused to believe his armies could have been defeated in a fair fight. He summoned the diviner Zhang Gong to ask whether another expedition was advisable; Zhang answered "no," and Kublai dissolved the expedition bureau (征東行省, seito shōshō). Two months later, however, he ordered the construction of 3,000 flat-bottomed ships and set August 1283 as the date for the next invasion — the desperation evident in a plan to conscript even Confucian students sitting their civil-service examinations. In May 1283 the campaign was suspended again as rebellions spread across former Southern Song territory and other regions, and the shipbuilders were sent home to the fields. By August, conscription and construction had resumed. Envoys dispatched to Japan turned back in storms or, in one case, were killed by a member of their own party upon reaching Tsushima — a clear sign of collapsing morale. An envoy named Jin Yuson (金宇孫), sent in 1293, was escorted all the way to Kamakura, where he was detained for the rest of his life without once managing to speak with a single Japanese person. ## The Limits of the Mongol Army — Losing When the Battlefield Changes Kublai's reign records only a handful of outright defeats — Japan, the Cham Kingdom (southern Vietnam), and the Mamluk Sultanate among them — but all share one feature: they were fought outside the steppe. Against Japan the barrier was the sea; against Southeast Asia it was the jungle. In the Cham campaign the Mongols brought horses but could not maneuver them in dense forest, and Champa ultimately refused to submit and preserved its independence. Epidemic disease in the humid climate compounded the losses severely. Fukai (深井), one of the podcast hosts, frames this as a "field battle" problem: even the most formidable army loses when forced onto unfamiliar terrain. Maritime expeditions — an "unusual project" for a steppe power — degraded the Mongols' situational awareness, which in turn produced misjudgments like accepting the "we lost to the storm" narrative at face value. ## Hōjō Tokimune's Sudden Death and the Question of Succession In 1284 (Kōan 7), Regent (shikken) Hōjō Tokimune (北条時宗), who had led Japan's response to the Mongol threat, suddenly collapsed and died five days later at the age of 34. Records show he had been carrying out normal duties right up until the end — a sign of how deeply he had been worn down. He had become rensho (co-signer) at 14, shikken at 18, and over the following sixteen years survived two Mongol invasions while endlessly struggling to concentrate power and manage unresolved reward disputes. His successor was his 14-year-old son, Hōjō Sadatoki (北条貞時). Adachi Yasumori was among the first to back him. Turbulence within the Hōjō clan — coinciding in timing with the Nayan–Kaidu revolts — made this a perilous moment; it is widely held that a third Mongol attack during this window would have been extremely dangerous for the shogunate. ## The Kōan Tokusei Decree — Adachi Yasumori's Political Reforms The political reform program that Tokimune had reportedly been planning was carried through by Adachi Yasumori under the name Kōan Tokusei Decree (弘安の徳政令). Its more than 90 articles centered on several pillars. **Shogun Sadatoki's vow of frugality** (cultivating virtuous leadership): the author of the tokusei embraces austerity himself to build political legitimacy. **Establishing the shogun's economic base**: strengthening direct landholdings to restore genuine shogunal authority. **Incorporation of non-gokenin into the gokenin class**: warriors who fought in the Battle of Kōan but held no formal status were enrolled as gokenin, giving them standing to petition the shogunate when lawless actors seized their land. **Suppression of akutō and gamblers**: addressing deteriorating public order. **Tax relief and improved litigation procedures**: protecting the livelihood of gokenin. **Restoration of shrine and temple lands**: land in Kyushu that had been sold off was permitted to revert to its original religious owners. Because the reforms aimed to restore shogunal authority, retainers whose fortunes were tied to the Hōjō regent's house pushed back, producing open internal conflict. ## The Ideology of "Tokusei" — A Revolution with Its Teeth Pulled The term tokusei means "virtuous governance" and draws on two strands of Confucian thought. The first is the Heaven-and-humanity correspondence theory (天人相関説) systematized by the Han-era scholar Dong Zhongshu: earthquakes, eclipses, and other disasters are caused by the ruler's lack of virtue. The second is Mencius's mandate revolution theory (易姓革命説): if a ruler remains unvirtuous, the people have the right to overthrow the ruling house and install a new one. One striking feature of the aftermath of the Mongol invasions is that they were interpreted as natural disasters rather than man-made threats. Fukai identifies this as characteristic of a people with no prior experience of a serious external enemy: treating the invasions as acts of Heaven removes the need to analyze the opponent and encourages a passive acceptance of the uncontrollable. When the mandate revolution theory reached Japan it was effectively defanged. The original idea — that an unvirtuous ruler may be replaced by another family — was converted into the far milder program of practicing frugality and enacting good governance. Fukai compares this to how Halloween was adopted in Japan: the original meaning is discarded and only the convenient surface is absorbed. The aristocracy and religious establishments interpreted the Kōan victory as a product of their own prayers rather than samurai valor, and demanded rewards from the shogunate accordingly. Shrines argued that the Mongol invasion had been divine punishment for the defilement of shrine lands, making the Tokusei Decree's land restoration both a spiritual obligation and an opportunity to reclaim lost property. ## Takeaways - Kublai never abandoned his goal of conquering Japan, ordering 3,000 warships and dispatching envoys right through 1293, even as rebellions and storms repeatedly derailed his plans. - Hōjō Tokimune died at 34 just three years after the Battle of Kōan, and the sweeping Kōan Tokusei Decree — led by Adachi Yasumori — was enacted under his 14-year-old successor, Hōjō Sadatoki. - The concept of tokusei draws on Dong Zhongshu's Heaven-humanity correspondence and Mencius's mandate revolution theory, but in Japan the revolutionary clause was stripped away, leaving only frugality, good governance, and the restoration of shrine lands.