In the year 591, the ill-fated Emperor Sushun conceived the idea of sending a large army to re-establish his country's prestige in the peninsula, but his own assassination intervened, and for the space of nine years the subject was not publicly revived. Then, in 600, the Empress Suiko being on the throne, a unique opportunity presented itself. War broke out between Shiragi and Mimana.
It has been shown how, in A.D. 562, the Japanese settlement in Mimana was exterminated; how the Emperor Kimmei's dying behest to his successor was that this disgrace must be removed; how subsequent attempts to carry out his testament ended in failure, owing largely to Japan's weak habit of trusting the promises of Shiragi, and how, in 618, the Sui Emperor, Yang, at the head of a great army, failed to make any impression on Korea.
She asked that four regions, forming an integral part of the Yamato domain of Mimana, should be handed over to her, apparently as an act of pure benevolence. Japan consented. There is no explanation of her complaisance except that she deemed it wise policy to strengthen Kudara against the growing might of Shiragi, Yamato's perennial foe.
Sushun was placed on the throne as a concession to appearance, but, at the same time, he was surrounded with creatures of the o-omi, so that the latter had constant cognizance of the sovereign's every word and act. When the o-omi judged the time fitting, he proposed to the Emperor that an expedition should be despatched to recover Mimana, which had been lost to Japan some time previously.
In response to Shiragi's overtures, the King of Koma sent a body of troops to assist in protecting that principality against any retaliatory essay on the part of the Japanese in Mimana. But the men of Shiragi, betrayed into imagining that these soldiers were destined to be the van of an invading army, massacred them, and besought Japanese succour against Koma's vengeance.
They withdrew their forces, but no sooner had their ships passed below the horizon than Shiragi once more invaded Mimana. It seemed at this juncture as though the stars in their courses fought against Japan. Something, indeed, must be ascribed to her own methods of warfare which appear to have been overmerciful for the age.
To these appeals the Yamato Court lent a not-unready ear, partly because they pleased the nation's vanity, but mainly because Kudara craftily suggested danger to Mimana unless Japan asserted herself with arms. But when it came to actually rendering material aid, Japan did nothing commensurate with her gracious demeanour.
But one great captain, Pok-sin, saved the situation. Collecting the fugitive troops of Kudara he fell suddenly on Shiragi and drove her back, thereafter appealing for Japanese aid. At the Yamato Court Shiragi was now regarded as a traditional enemy. It had played fast and loose again and again about Mimana, and in the year 657 it had refused safe conduct for a Japanese embassy to the Tang Court.
The two officials by whose advice the throne made this sacrifice were the o-muraji, Kanamura, and the governor of Mimana, an omi called Oshiyama. They went down in the pages of history as corrupt statesmen who, in consideration of bribes from the Kudara Court, surrendered territory which Japan had won by force of arms and held for five centuries. This proved an ill-judged policy.
But as the material development of Japan and her civilization progressed, she stood constantly to lose more and gain less by despatching expeditions to a land which squandered much of its resources on internecine quarrels and was deteriorating by comparison. The task of maintaining Mimana and succouring Kudara then became an obligation of prestige which gradually ceased to interest the nation.