In 395 A.D., King Gwanggaeto of Goguryo conquered Paeryo in the area of Siramuren river. In that time, Later-Yan gone into war with Northern Wei. Northern Wei invaded territory of Later-Yan in march of 395 A.D. Northern Wei defeated utterly Later-Yan in Chamhabpa of Eastern Mongolia.
In 385 A.D., Goguryo had a war with Later-Yan for taking Yodong.. After the war between Goguryo and Later-Yan, both countries became potential enemies for each other.
Later-Yan had a battle with Northern Wei In 395 A.D. At that time, King Gwanggaeto conquered Paeryo without check of Later-Yan. Goguryo obtained flocks of sheep, horses and cattle. These material resources were used attack on Baekje.
After conquest of Paeryo, King Gwanggaeto of Goguryo made a round of Yodong for hunting.
In that time, Yodong was territory of Later-Yan. Later-Yan raise an large scale army against Northern Wei. In the face of these situations, the Goguryo forces could understand topograpies and planimetric feat1ures of Yodong area.
Meanwhile, this theses takes note of relationship between Goguryo and Later-Yan. Goguryo employed a foreign policy in which it maintained the installation relationship with Later-Yan in 396 A.D.. At this time, Later-Yan was consistently attacked by Northern Wei.
In this situation, if Goguryo had invaded in Later-Yan, Later-Yan had to raise the tomahawk with Goguryo and Northern Wei. On this reason, Later-Yan used installation relationship as a safety device. On one hand, Goguryo accepted installation relationship. Why did accept Goguryo installation relationship from Later-Yan? Because Goguryo was admitted the dominium in the region of Pyeongju, Yodong and Daebang by Later-Yan.
Also, It had relevance to a relation with Baekje. Goguryo captured 58 castles and 700 country of Baekje in 396 A.D. In this situation, Goguryo could concentrated on attacking Baekje without unawaring of Later-Yan.