The unification of the Three Kingdoms by Silla in 676 led to the North South States Period, in which much of the Korean Peninsula was controlled by Later Silla, while Balhae controlled the northern parts of Goguryeo. Balhae was founded by a Goguryeo general and formed as a successor state to Goguryeo. During its height, Balhae controlled most of Manchuria and parts of the Russian Far East, and was called the Prosperous Country in the East. Later Silla was a golden age of art and culture, as evidenced by the Hwangnyongsa, Seokguram, and Emille Bell. Relationships between Korea and China remained relatively peaceful during this time. Later Silla carried on the maritime prowess of Baekje, which acted like the Phoenicia of medieval East Asia, and during the 8th and 9th centuries dominated the seas of East Asia and the trade between China, Korea and Japan, most notably during the time of Jang Bogo; in addition, Silla people made overseas communities in China on the Shandong Peninsula and the mouth of the Yangtze River. Later Silla was a prosperous and wealthy country, and its metropolitan capital of Gyeongju was the fourth largest city in the world. Buddhism flourished during this time, and many Korean Buddhists gained great fame among Chinese Buddhists and contributed to Chinese Buddhism, including: Woncheuk, Wonhyo, Uisang, Musang, and Kim Gyo-gak, a Silla prince whose influence made Mount Jiuhua one of the Four Sacred Mountains of Chinese Buddhism. However, Later Silla weakened under internal strife and the revival of Baekje and Goguryeo, which led to the Later Three Kingdoms period in the late 9th century.