Theme: Korea Plan

North–South States Period
Beginning in the 6th century, Silla's power gradually extended across the Korean Peninsula. Silla first annexed the adjacent Gaya confederacy in 562. By the 640s, Silla formed an alliance with the Tang dynasty of China to conquer Baekje and later Goguryeo. After conquering Baekje and Goguryeo, Silla repulsed Tang China from the Korean peninsula in 676. Even though Silla unified most of the Korean Peninsula, most of the Goguryeo territories to the north of the Korean Peninsula were ruled by Balhae. Former Goguryeo general or chief of Sumo Mohe Dae Jo-yeong led a group of Goguryeo and Mohe refugees to the Jilin and founded the kingdom of Balhae, 30 years after the collapse of Goguryeo, as the successor to Goguryeo. At its height, Balhae's territories extended from southern Manchuria down to the northern Korean peninsula. Balhae was called the "Prosperous Country in the East".

Unified Silla and Balhae in the 8th century CE
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. Later Silla was a golden age of art and culture, as evidenced by the Hwangnyongsa, Seokguram, and Emille Bell. 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.
Later Silla fell apart in the late 9th century, giving way to the tumultuous Later Three Kingdoms period (892–935), and Balhae was destroyed by the Khitans in 926. Goryeo unified the Later Three Kingdoms and received the last crown prince and much of the ruling class of Balhae, thus bringing about a unification of the two successor nations of Goguryeo.