This thesis is written to clarify the shift in the confrontation line of the mid-upper Geum River valley and the strategy of Three Kingdoms in terms of tactics followed by Goguryeo's surrendering Han-fortress, Baekje.Main force units of the Goguryeo withdrew from the position right after the collapse, some of the force remained to command Asan coast-Baekma ridge line based on the Mongchontoseong as the strategic point. Baekje transferred its capital to Ungjin to rebuild a dynasty supported by Silla. Goguryeo maintained the dominance by oppressing the Geum River's mid valley and the Miho stream valley－a branch stream of Geum River－through the Cheonan and the down stream of Namhan River, respectively. Silla secured the Miho stream valley as the strategic place and supported the defense of the nearby Miho valley at the same time. The Silla-Baekje Allied switchover from restrictive cooperative relationship to destinies military alliance.Baekje advanced to the Hansan fortress in contraposition with Goguryeo military with the help of cooperation of the Wae-Silla until 482. To make an example of this, Goguryeo attempted to make a raid on the capital of Silla, which ended up a failure. However, Goguryeo procured an advance base in the Namseonggol Fortress, Jungwon and Weolpyungdong, Daejeon through the Miho stream basin in about 484, which resulted in the cut off between the Baekje and Silla, recovering the overwhelming dominance over those two countries.Henceforth, both nations of Silla-Baekje laid stress on the defense against the Goguryeo. Though, Baekje founded the stepping stone to the stable development by recovering the Miho stream basin until 494. Silla stabilized its control over the upper Geum River as well as put pressure on the upper Namhan River valley. Goguryeo took a turn for the better preservation of the strong point in the Namhan River valley. In consequence, Three Kingdom's confrontation line maintained its relative stability until the violent collision between the Three Kingdoms around the Han River valley in the 6th mid-century.