Geunchogo of Baekje, Chogo II of Baekje (324–375, r. 346–375) was the 13th king of Baekje, one of the Three Kingdoms of Korea. He reigned over the apex of Baekje's powers. Background Geunchogo was the fourth son of the 11th king Biryu and became king upon the death of the 12th king Gye. His reign seems to have marked the permanent ascendancy of the descendants of the 5th king Chogo (reflected in Geunchogo's name) over those of the 8th king Goi, and ended the alternating kingship of the two lines. Strengthening royal power Upon ascending the throne, he set out to solidify the royal power within the Baekje state. He reduced the power of the aristocracy and set up a system of local government with regional heads appointed by the court. He married a wife from the Jin clan, setting a precedent for his successors, and he moved the capital to Hansan, today's southeast Seoul. Territorial expansion Under Geunchogo, the kingdom reached its greatest geographic extent and political power. The remaining tribes of Mahan were annexed in 369, completing Baekje's control over all of present-day Jeolla-do. Gaya confederacy states west of the Nakdong River were also made Baekje dependencies. In 369, Baekje was invaded by Goguryeo, but counterattacked in force at the Battle of Chiyang. In 371, the Baekje army of 30,000, led by Crown Prince Geungusu, took the fortress of Pyongyang and killed Gogugwon of Goguryeo. At the end of these conquests, Baekje ringed the Yellow Sea, and controlled much of the Korean peninsula, including all of Gyeonggi, Chungcheong, and Jeolla and parts of Gangwon and Hwanghae provinces. Foreign relations In 366, Geunchogo allied with Silla, which bordered Baekje on the east, maintaining a rough balance of power among the Three Kingdoms. At its greatest extent, Baekje control reached north into what is now China. The kingdom also established diplomatic relations with the early Jin China in 345 and Japan in 367. According to both Korean and Chinese sources, the first diplomatic contact between Baekje and China took place in 372, when Geunchogo sent a mission to the court of Jin. In the same year, the Jin court sent a mission granting him the title of the "General Stabilizing the East and the Administrator-General of Lelang" (진동장군 영낙랑태수, 鎭東將軍領樂浪太守). During his reign, Baekje activated and led the commercial trading among China, Korean Peninsula and Japan; known as the triangle