During the 4th century, Geunchogo expanded Baekje's territory to the north at the expense of Goguryeo. In 369, Gogukwon, the monarch of Goguryeo, attacked Baekje with 20,000 troops, but was defeated by Crown Prince Geungusu at the Battle of Chiyang. In 371, Geungusu led 30,000 troops and attacked the fortress of Pyongyang, slaying Gogukwon in battle. Baekje was a powerful maritime nation whose influence extended across the sea to Liaoxi and Shandong in China, taking advantage of the weakened state of Former Qin, and Kyushu in the Japanese archipelago.