天皇が二人いた時代：南北朝の概観Strange Era When Two Emperors Coexisted

During the Nanbokucho Period (南北朝時代, 1336–1392), a peculiar era emerged in Japan when two emperors coexisted, each asserting their own legitimacy. Emperor Go-Daigo (後醍醐天皇, 1288–1339), the 96th emperor who played a central role in the overthrow of the Kamakura Shogunate, had, as previously discussed, a naive perception of his times. This misjudgment led him to incur intense resentment from the samurai class soon after his successful revolution, resulting in the collapse of his administration within just two years. Amid this chaos, Takauji Ashikaga (足利尊氏, 1305–1358), a prominent figure among the gokenin (御家人, vassals) of the Kamakura Shogunate, became one of the first to grow disillusioned with Emperor Go-Daigo’s attempt to restore Heian-era aristocratic dominance. Consequently, he distanced himself from the emperor and plotted the establishment of a new samurai-led government.

Initially loyal to Emperor Go-Daigo, Takauji Ashikaga eventually rebelled against Go-Daigo’s faction, swiftly allying himself with Emperor Kogon (光厳天皇, 1313–1364) to defeat Yoshisada Nitta (新田義貞, 1301–1338), Go-Daigo’s leading military supporter, thereby collapsing Go-Daigo’s regime. This led to a division of Kyoto into two factions. However, Takauji Ashikaga’s side, which had effectively gathered the discontent of the samurai class, swiftly grew dominant, forcing Emperor Go-Daigo out of Kyoto. Emperor Go-Daigo retreated to Yoshino in Nara Prefecture. After ousting Go-Daigo from Kyoto, Takauji Ashikaga and Emperor Kogon swiftly consolidated power in the capital by enthroning Emperor Komyo (光明天皇, 1322–1380), asserting legitimacy for their faction. Thus began the peculiar era of two emperors—the Southern Court (南朝, Nancho) and the Northern Court (北朝, Hokucho).

The Southern Court, allied with Emperor Go-Daigo, established its court in Yoshino, Nara Prefecture, while the Northern Court, supported by Takauji Ashikaga, continued its governance from Kyoto under Emperors Kogon and Komyo. Japan’s samurai class faced the difficult choice of allegiance between these two rival courts, resulting in a profound regional divide across the Kansai region. Yet, the roots of this imperial split trace back not to this immediate confrontation but to events late in the Kamakura period. Old resentments, simmering since that time, erupted following the fall of the Kamakura Shogunate, exploited politically by Takauji Ashikaga, further deepening the conflict.

This bitterness traces back to 1258 when retired Emperor Go-Saga (後嵯峨上皇, 1220–1272) held the authority to designate imperial successors. Internal disputes arose during the nomination of the crown prince (皇太子, Kotaishi), who was to become the legitimate imperial successor. A pivotal moment occurred upon Go-Saga’s death in 1272 when his will notably lacked any explicit instructions regarding his successor, instead deferring the decision to the authority of the Kamakura Shogunate. This omission fueled a rivalry between brothers Emperor Go-Fukakusa (後深草天皇, 1243–1304), the elder son of Go-Saga and Kitsushi Saionji (西園寺姞子, 1225–1292), and his younger brother Prince Tsunehito (恒仁親王), who would later become Emperor Kameyama (亀山天皇, 1249–1305).

Initially, Emperor Go-Fukakusa ascended the throne in 1246 at age four after Emperor Go-Saga abdicated in his favor. However, in 1258, under significant pressure from Go-Saga, who effectively held supreme authority over the imperial court, Go-Fukakusa’s younger brother, Prince Tsunehito, was appointed as crown prince. By 1259, following an illness, Go-Fukakusa was compelled to abdicate in favor of his brother, who then ascended the throne as the 90th emperor, Emperor Kameyama. Notably, it is widely believed that their parents greatly favored Emperor Kameyama, and this preferential treatment laid the foundation for future strife.

After abdicating, the retired Emperor Go-Fukakusa fathered a son whom he intended as his successor. Nevertheless, in 1268, Go-Saga chose instead a son from Emperor Kameyama’s lineage as crown prince, fueling further animosity between the brothers. Upon Go-Saga’s death in 1272, with no authority left to mediate, the rivalry between Go-Fukakusa and Kameyama escalated into open conflict over imperial succession. However, given the imperial court’s diminished political authority at the time, the matter was ultimately referred to the Kamakura Shogunate, controlled by the Hojo clan (北条氏), in accordance with Go-Saga’s will.

The Shogunate then turned to Kitsushi Saionji, the mother of both emperors, asking which of her sons Go-Saga truly favored. Kitsushi, due to her profound affection for Emperor Kameyama, named him as Go-Saga’s favored successor. Thus, the Kamakura Shogunate officially recognized Kameyama as the legitimate emperor. Emperor Kameyama continued his reign until 1274, when he abdicated in favor of his own son, who then ascended the throne as Emperor Go-Uda (後宇多天皇, 1267–1324), the 91st emperor.

During this period, however, Retired Emperor Go-Fukakusa’s dissatisfaction only deepened. Through relentless scheming and persistent lobbying of the Kamakura Shogunate, Go-Fukakusa succeeded in having one of his own sons officially designated as crown prince by the shogunate in 1275, thereby securing the promise of regaining control over the imperial household in the future.

This development intensified the rivalry between the two factions, placing the Kamakura Shogunate squarely between them. Since the authority of the Hojo clan, the shogunate’s ruling family, had already begun to weaken at this stage, the shogunate feared that continued turmoil within the imperial court could destabilize its own governance. Thus, it issued a compromise decision, whereby descendants from each imperial lineage would alternate the imperial throne approximately every ten years, jointly managing the court’s affairs.

This compromise, however, created a distorted fissure within the structure of the imperial household, one which resurfaced prominently during the chaotic collapse of the Kamakura Shogunate. This alternating succession system functioned well while the shogunate’s authority remained intact, but as the shogunate gradually weakened, imperial factions regained momentum, leveraging this rivalry to justify their revolt against the Kamakura regime. The central figure among these factions who ascended the throne during this turbulent period was Emperor Go-Daigo. Notably, the upheaval of this period resembles the political turmoil during the Meiji Restoration at the end of the Edo period.

At the core of the issue was Emperor Go-Daigo’s decision to disregard the shogunate’s ruling on imperial succession from the 1270s, aiming instead to place his own lineage as the sole legitimate imperial line. This maneuver split the imperial court into two opposing factions. To divert attention away from this internal imperial dispute, Go-Daigo and his supporters channeled public resentment toward the overthrow of the Kamakura Shogunate, plunging the nation into the turmoil of the Nanbokucho Period. Consequently, the imperial family split into two lineages—the Southern Court and the Northern Court—each vying for legitimacy. This outlines the essence of the Nanbokucho Period: old grudges already existed, but Emperor Go-Daigo, who lacked awareness of the broader political landscape, became the catalyst that ignited this explosive conflict.

Looking objectively at the situation, the Northern Court had been supported since 1338 by Takauji Ashikaga’s newly established Muromachi Shogunate (室町幕府), which wielded substantial power and influence. It might therefore seem that the Northern Court should not have needed to assert its legitimacy aggressively. However, the situation was complicated by the fact that the Southern Court had secured a vital symbol traditionally used to demonstrate imperial legitimacy—the sacred regalia known as the Sanshu-no-Jingi (三種の神器, Three Imperial Regalia). Imperial legitimacy fundamentally depended on possessing these sacred items, and without them, an emperor’s claim to the throne was invalid, rendering him effectively a false emperor.

The fact that Emperor Go-Daigo fled to Yoshino with the Sanshu-no-Jingi significantly strengthened the Southern Court’s position. The Northern Court found itself unable to decisively defeat the Southern Court precisely because the Southern Court retained this crucial legitimacy. Given the supreme importance of legitimacy within the imperial tradition, many samurai eventually sided with the Southern Court due to its possession of the sacred regalia, enabling it to resist ongoing pressure from the shogunate-backed Northern Court.

But what exactly are these Sanshu-no-Jingi? This crucial topic will be explored in our next article.