仏教受容を巡る蘇我氏と物部氏Turning Point of Buddhism Taking Root in Japan

In the mid-6th century, Buddhism, which had been Sinicized through the Korean kingdom of Baekje, is said to have been officially introduced to Japan. At the time, this new development triggered a significant debate within the imperial court regarding the acceptance of Buddhism, eventually leading to events that radically altered the historical landscape. Central to this debate were two powerful clans: the Soga, who advocated accepting this new religion, and the Mononobe, who opposed it vehemently, favoring traditional indigenous beliefs.

However, the conflict between the Soga and Mononobe clans extended beyond mere differences in religious views. Viewed from another perspective, this struggle represented a critical turning point in Japanese history—a political power contest in the Yamato region (present-day southern Nara Prefecture)—marked by a shift in dominance from the traditional Mononobe clan to the rising Soga clan, who adeptly leveraged continental (mainly Chinese) cultural influence.

Tracing the origins of this conflict, around the year 552, during the reign of the 29th emperor, Kinmei (欽明天皇, 539–571 CE), King Seong of Baekje presented the emperor with Buddhist scriptures, teachings, and a statue of Shakyamuni Buddha. The emperor consulted his senior advisors on whether to accept this new faith. At this juncture, a prominent noble, Soga no Iname (蘇我稲目, 506–570), argued fervently in favor of venerating the Buddha statue. Conversely, Mononobe no Okoshi (物部尾輿), head of the venerable Mononobe clan, and Nakatomi no Kamako (中臣鎌子) strongly opposed, claiming that worshiping foreign kami would anger Japan’s native deities. This division sharply split the imperial court. Given the strong influence of the Shinto faction at this point, the emperor refrained from making a decisive judgment. Instead, he entrusted the Buddha statue to Soga no Iname, who showed initial openness toward Buddhism, permitting the Soga clan to practice the new faith experimentally. For the emperor, this was partly to evaluate the impact of Buddhist worship on traditional Shinto beliefs.

Behind the Soga clan’s proactive stance toward Buddhism was not merely religious devotion, but a significant divergence in political and cultural orientation from traditional clans. The Soga clan had a pronounced interest in China and Korean cultures, maintaining close relations particularly with immigrant groups residing primarily in the Asuka region under their control. At the time, Buddhism was essentially a comprehensive package of cutting-edge ideas and culture imported from the continent. Naturally, establishing temples and creating Buddhist statues required advanced technology and significant resources. Soga no Iname saw early exposure to these advanced technologies and knowledge as an ideal opportunity to elevate his clan’s prestige, eventually seize the reins of the imperial court, and supplant the older powerful clans.

Indeed, the Soga clan’s leadership in Buddhism’s introduction prompted an increase in state-sponsored projects such as temple construction, creating employment opportunities for many. Immigrants, who typically found it difficult to secure stable work, particularly benefited from this. Thus, from the Yamato court’s governance perspective, the Soga clan’s approach proved convenient. As Soga influence grew, regional chieftains began to perceive greater tangible benefits from aligning with the Soga, thinking, “Siding with the Soga means increased public works and profits, whereas siding with the Mononobe yields few rewards.” This practical calculation contributed significantly to support for the Soga faction. Hence, it is critical to understand that the division between pro-Buddhism (Soga clan) and anti-Buddhism (Mononobe clan) factions involved pragmatic considerations beyond purely religious perspectives.

Upon obtaining Emperor Kinmei’s approval, Soga no Iname first enshrined the Buddha statue at his residence, the Oharida Palace in Asuka, beginning active worship. Additionally, Iname converted his separate residence at Mukuhara into a temple site, constructing a small hall that marked Japan’s first known Buddhist temple. While this initial “temple” was far simpler than the grand tile-roofed temples later built—consisting merely of a hall for placing the Buddha statue within a residence—it was nonetheless groundbreaking in establishing Buddhism’s presence in Asuka. This residential temple, named Kogenji (向原寺), later relocated and evolved significantly over time, eventually becoming Sakuraiji (桜井寺) during the reign of the 30th Emperor, Bidatsu (敏達天皇, 572–585), and Toyura-dera (豊浦寺) during the reign of the 33rd Emperor, Suiko (推古天皇, 593–628). From these modest beginnings, the Soga clan systematically fostered Buddhism’s institutional roots in Japan.

We cannot overlook the significant role played by immigrant craftsmen and technical specialists in supporting the Soga clan’s efforts to promote Buddhism. In fact, Buddhism did not initially take hold in Japan simply because of fervent indigenous belief. The Soga held prominent administrative positions, responsible for finances and diplomacy, and were local rulers who had integrated immigrant communities and their descendants into their political power structure. For instance, a notable immigrant group called the Yamato no Aya (東漢氏) served the imperial court. This group was an umbrella term for various clans originating from China and the Korean peninsula, skilled especially in ironworking, harness-making, and civil engineering. The Yamato no Aya traced their ancestry back to Chinese imperial lineage and contributed significantly to early Japanese state formation alongside the Soga during Buddhism’s rise in the Asuka period. Thus, the empowerment of the Soga clan rested heavily on skilled groups such as the Yamato no Aya, whose contributions helped the Soga reshape the balance of power at court.

Indeed, Soga no Umako (蘇我馬子, 551–626), son of Iname, was able to envision creating a new Buddhist-based state precisely because of the Soga clan’s unique ability to skillfully organize and utilize these technologically advanced immigrant groups from early on. The Soga demonstrated notable political acumen in bringing together people of differing languages and customs, and channeling their advanced skills and knowledge effectively into temple-building projects and water management initiatives.

In addition, we cannot overlook a previously proposed hypothesis suggesting that the Soga clan’s fervent embrace of Buddhism stemmed from their own immigrant origins. This theory, put forth by ancient-history scholar Teiji Kadowaki and others in the 1970s, speculated that the Soga clan descended from immigrant groups from Baekje (a Korean kingdom), triggering intense scholarly debate. Subsequent studies, however, rarely offer direct support for the immigrant-origin theory today, generally favoring instead the view that the Soga were one of the indigenous powerful clans. Of course, this scholarly context has been significantly shaped by prewar ideologies promoting the concept of Japan as a homogeneous nation. Indeed, historical records such as the Nihon Shoki and genealogical sources state that the Soga clan descended from the “Katsuragi / Kazuraki clan” (葛城氏) or perhaps shared distant kinship with the imperial family itself. Though the exact lineage of the Soga clan remains unclear, during my own research in Nara, I have begun to consider another possibility.

Importantly, it is well recognized today that even the Katsuragi clan itself had immigrant roots. Presently, a place named Katsuragi City remains in Nara Prefecture, historically serving as the Katsuragi clan’s stronghold. Archaeological discoveries in this region suggest strongly that the clan originated abroad. However, the perspective of directly viewing the Soga clan as foreign is still not mainstream within Japan. Recently, instead, there has been scholarly discussion regarding the possibility that the Soga and Nakatomi clans branched off as royal lineages related to the imperial household. Given that many documents detailing the origins of the Soga clan were destroyed during their later downfall, it is impossible today to conclusively determine their precise ancestry.

Eventually, the conflict between the Soga and Mononobe clans over the acceptance of Buddhism intensified into a severe confrontation. Although the debate remained relatively nonviolent during Emperor Kinmei’s reign, circumstances changed dramatically under the subsequent Emperor Bidatsu. A pivotal figure at this juncture was Soga no Umako, who inherited his father Iname’s commitment to promoting Buddhism. Personally, I believe that without Soga no Umako’s emergence, Buddhism might never have gained its historical influence within Japan—he was that significant.

Soga no Umako attempted once again to propagate Buddhism under Emperor Bidatsu. However, around 584 CE, a devastating epidemic swept through Yamato, killing countless people. Mononobe no Okoshi and Nakatomi no Kamako, key anti-Buddhist figures, saw this as an opportunity to suppress the rising Soga power and presented a strategic argument to the emperor. They claimed the epidemic was caused by the wrath of indigenous kami angered by Buddhism’s introduction, arguing that unless Buddhist statues were immediately destroyed and prayers offered to native kami, disaster would continue. Emperor Bidatsu, who remained uncertain about Buddhism’s acceptance, reversed his stance and issued an edict prohibiting Buddhism. Consequently, officials aligned with anti-Buddhist factions within the court destroyed the temples under Soga control, transporting the imported gilt-bronze Buddha statue to Horie in Naniwa (an ancient canal near modern-day Osaka Bay) and disposing of it into the sea. Thus, Japan’s first Buddhist temple was reduced to ashes, and its Buddha statue sank beneath the ocean.

For the Soga, who considered Buddhism crucial to shifting the court’s internal balance of power, this event was a severe setback. Recognizing the changed circumstances, Soga no Umako outwardly ceased Buddhist activities. Yet, curiously, another significant event soon occurred, an inexplicable disaster that turned sentiments back toward Buddhism.

According to the Nihon Shoki, immediately after anti-Buddhist factions burned down the temples, a sudden fire erupted in the emperor’s palace on a clear and windless day. At the time, Yamato housed many immigrant groups, who symbolically interpreted this disaster as divine retribution from the discarded Buddha. Intriguingly, this period marks the explicit recognition by the Mononobe and Nakatomi clans of indigenous Shinto deities as “native kami” in contrast to Buddhism’s status as “foreign kami.” Rumors spread that disrespecting the Buddhist statues had brought punishment, gradually shifting the tide of the era. Naturally, it is plausible to assume that this mysterious fire could have been orchestrated by the Soga faction, aiming to restore their influence.

In other words, while the epidemic outbreak was seen as punishment from indigenous kami angered by Buddhism’s acceptance, prompting anti-Buddhist action, the mysterious fire immediately afterward was viewed as “punishment for rejecting Buddhism” or “the Buddha’s retribution.” Although superficially this turmoil involved fears over epidemics and religious debates about whether to trust native deities or Buddhism, beneath the surface, as repeatedly emphasized, lay a politically motivated struggle for dominance under the guise of religious conflict. Succinctly, the era can be understood as an emblematic clash between “indigenous kami” and “new foreign kami (Buddhism),” where power struggles played out against the backdrop of disasters like epidemics and fires.

From this point forward, the situation dramatically shifted in favor of the pro-Buddhist faction. To offer my own interpretation, Buddhism’s extensive historical impact in Japan hinged critically upon two decisive factors: the “mysterious fire” and the “rise of Soga no Umako.” When these two transformative elements converged, Japan’s turbulent Buddhist history truly began.