The was a war of succession that took place in the Yamato Kingship near the end of Asuka period. It broke out in 672 following the death of Emperor Tenji. The name refers to the jinshin (Ch. renshen 壬ç³) or ninth year of the sexagenary cycle, corresponding to the Gregorian year 672. It was one of the largest conflicts in classical Japanese history.
Tenji had designated his brother, Prince à Âama, as his successor, but later changed his mind in favor of his son, Prince à Âtomo. In the course of the violence that erupted as a result of factional rivalries, à Âtomo, having taken the throne as Kà Âbun, killed himself after reigning for less than a year. His uncle à Âama then succeeded to the throne as Emperor Tenmu. Tenmu was the first monarch of Japan contemporaneously documented as using the title
After the defeat of Baekje and their Yamato allies by Silla and Tang China in the Battle of Baekgang, Emperor Tenji, in defiance of opposition from his retainers, moved his capital to à Âmi à Âtsu Palace (now in à Âtsu, Shiga Prefecture), and prepared to respond to the growing threat from East Asia. He attempted to build a stronger centralized state, mimicking the Tang's bureaucracy, importing their political systems and legal codes, consequently affecting Japanese culture as a whole. Emperor Tenji is credited with compiling the à Âmi Code, the first collection of Ritsuryà  laws, widely regarded as the earliest legal codes in Japan. Japan was under a process of political unification by the Yamato clan, seeking to dissolve the powerful hegemony of local prestigious clans in the Uji clan system.
The next task Tenji needed to address was that of securing his successor. His empress consort, Yamato hime, had borne no children. He had to find a successor among the sons of non-imperial wives. Prince Takeru, the eldest son, was mute from birth and died at age seven. Prince à Âtomo was the next prince; he was diligent and brilliant. He had enough ability to be the next emperor. Although à Âtomo was almost perfect, he was not born into the Imperial Household. His mother was of low birth from a rural landlord's family. This was a significant disadvantage to à Âtomo's candidacy for the throne.
However, there was another candidate who was as excellent as à Âtomo: the emperor's younger brother, Prince à Âama, who was equally capable. His reputation was much greater than à Âtomo's because he was of higher birth and thus more suitable to be emperor. This was a major cause of the subsequent trouble. à Âtomo was also known for his martial prowess.
In 670, Emperor Tenji grew ill. Realizing he would not live much longer, he wished that, after his death, the throne would pass to his favorite son, Prince à Âtomo, who was appointed as the first Daijà Â-daijin (Chancellor of the Realm) in 671. Because à Âtomo's greatest rival was à Âama, the emperor attempted to drive the younger brother away; he invited the prince to his bedroom and asked if à Âama had an intention to take the throne. If à Âama answered yes, the emperor would have arrested and punished him as a traitor. However, the prince was clever enough to see through the trick and answered that he had no will to succeed to the throne, preferring that à Âtomo be the next emperor. He added that he wanted to become a Buddhist monk instead of inheriting the throne and would retire to a temple in Yoshino, Nara. Because there were no reasons to punish à Âama, the emperor accepted the prince's proposal. The next day, à Âama departed for Yoshino along with Tenji's daughter, Uno no Sarara (the future Empress Jità Â), to become a monk.
The emperor declared à Âtomo his successor. à Âtomo summoned six subjects to the emperor's bedroom and had them swear to help him in the presence of his father. Tenji nodded his assent, and several days later, he died.
After the emperor's death, Prince à Âtomo began his administrative activities as the new emperor. Soga no Akae (èÂÂæÂÂ赤å Â), Soga no Hatayasu (èÂÂæÂÂæÂÂå®Â), Kose no Omi Hito (å·¨å¢è£æ¯ÂçÂÂ), Ki no Ushi (ç´Â大人) and other subjects followed him.
Meanwhile, Prince à Âama pretended to be a monk at a temple in Yoshino, all the while looking for the opportunity to instigate a rebellion against his nephew and drive him away. He secretly began collecting weapons and soldiers. In June 672, after learning that the à Âmi court plotted to kill him, he raised an army and departed Yoshino, marching for the palace in à Âtsu, where the new emperor resided. He strengthened his army by rallying local clans as he advanced through Uda, Iga and Suzuka, many of whom were dissatisfied by reforms put into place by à Âtomo's father. On his way, he was reunited with his sons who had fled from à Âmi. His eldest son Prince Takechi notably distinguished himself during this conflict. To cut off reinforcements from the eastern provinces, Prince à Âama seized strategic checkpoints such as the Fuwa Barrier, controlling ingress to the Kinai region.
Many challenges stood in the way of à Âama's forces: in some counties, guerrilla attacks prevented their march forward for many days. Every time they faced such difficulties, however, they fought bravely and patiently, gaining supporters to their cause along the way.
Ultimately, the war lasted for about a month. The important old capital of Asuka, was seized by general à Âtomo no Fukei on behalf of à Âama. Then on August 22, the outnumbered à Âmi court forces made their final stand west of the Seta Bridge in à Âmi, but were defeated. After a desperate struggle, à Âama captured the capital. Prince à Âtomo escaped to Mount Nagara near the palace, where he strangled himself to death. The subjects who supported him were arrested by à Âama's troops, and were punished as war criminals. Many ancient clans were destroyed or fell into obscurity as a result of the war.
The victor eventually burnt the capital down and returned to Asuka, where he built the Asuka-Kiyomihara Palace and married Empress Uno no Sarara. à Âama (Emperor Tenmu), then instituted political and military reforms that consolidated imperial power and centralized governance with the emperor at its core. He was notably the first monarch of Japan contemporaneously documented as using the title Tennà  (emperor), Tenmu's predecessors were retroactively given the title by later generations.
The following dates are given in accordance with the Julian Calendar.