서기 475년, 고구려군의 공격을 받아 백제의 도읍 漢城이 함락되고 蓋鹵王이 죽었다. 아우 文周王이 즉위해 도읍을 熊津으로 옮기며 국력을 회복하려 애썼지만 3년 만에 암살되었고, 문주왕의 아들 三斤王도 즉위 3년째 15세의 나이로 죽었다. 東城王은 삼근왕을 이어 왕위에 올랐다. 아버지 昆支는 이미 문주왕을 돕다가 암살된 뒤였으며, 바다건너 倭國에서 나고 자라 국내에는 아무런 정치기반도 없던 10세 안팎의 어린 나이였다. 처음에는 유력귀족에게 일을 맡기고 사냥 등에만 몰두하는 듯하더니 20세 무렵에 이르자 정력적으로 활동하기 시작했다. 동성왕이 열심히 일할수록 유력한 신하들과 갈등이 생겼다. 서기 501년, 동성왕이 죽었다. 『三國史記』에 따르면, 새로운 도읍으로 고심하던 泗비에서 겨울사냥을 하던 중 자객에게 살해된 것이다. 배다른 언니인 武寧王이 왕위를 잇고, 衛士佐平 백加가 암살배후로 지목되었다. 동성왕이 오랜 측근인 백加를 加林城으로 파견하자 앙심을 품었기 때문이라고 했다. 그런데 『日本書紀』의 내용은 사뭇 다르다. 동성왕이 無道하므로 나라사람들이 제거하고 무령왕을 세웠다는 것이다. 동성왕은 대체 누구에게 암살되었을까? 측근인 백加였을까, 정체불명의 정적들이었을까? 백가는 억울한 희생양이었을 것이다. 그는 무령왕이 이끄는 토벌군에게 전혀 저항하지 않았을 뿐 아니라 동성왕의 죽음을 통해 어떠한 이익도 얻지 못했다. 오히려 목이 베인 뒤 白江에 던져졌다. 정치권력에 얽매이던 시절의 역사기록은 종종 사실을 왜곡했는데, 동성왕의 죽음에 대한 『삼국사기』 기록이 그에 해당한다고 생각한다.

In the year of 475 by the attack by Koguryeo the capital of the Bakje Kingdom was conquered and King Gaero(蓋鹵王) lost his life. Following successor King Munju(文周王) moved the capital to Ungjin (now Gongju in Chungcheongnamdo Province) and tried to rebuild the strength of the country but in vain; he was assassinated in the third year of his reign, and his son King Samgeun(三斤王) also died in his age of fifteen, three years after enthronement. King Dongseong(東城王) who spend his childhood in Japan without much knowledge of the domestic politics acceded to the throne in his age of ten. In the early years of his reign he seemed not to have had any interest in the power but when he entered in his twenties he suddenly became very active in politics. As more power he`s got, the worse became the tension between him and some powerful subjects. Then in 501 King Dongseong was suddenly killed. According to The History of Three Kingdoms(Samguksaki) he was killed during his winter hunting by unknown assassin. After him King Muryeong(武寧王) started ruling Bakje and Royal Guard Minister Baekga(백加) was spotted as the criminal. He was believed that because he was sent to the remote Karim Fortress(加林城) he became very hostile against the King and decided to get rid of him. But the record of Japan`s ancient book the Chronicle of Japan(Nihonshyoki) says that people of Bakje had got rid of him and had Muryeong to replace him because the King Dongseong did not accomplish the way of King. Then here remains the question; who indeed killed the King Dongseong? Baekga? or other enemies? It is uncertain that Baekga was behind the conspiracy, because he did not resist against the royal army who came to kill him, and it didn`t seem that he had some benefits from the killing of the King Dongseong. The description of him in the History of Three Kingdoms can possibly be a result of political changes.