Northern as well as Southern States period

The Northern & Southern States period 698–926 CE is a period in Korean history when Unified Silla & Balhae coexisted in the south and north of the peninsula, respectively.

Unified Silla

After the unification wars, the Tang Dynasty established territories in the former Goguryeo, and began to administer and creation communities in Baekje. Silla attacked the Chinese in Baekje and northern Korea in 671.

The Tang Dynasty then invaded Silla in 674 but Silla defeated the Tang army in the north. Silla drove the Tang forces out of the peninsula by 676 tounification of nearly of the Three Kingdoms.

Unified Silla was a golden age of art and culture, and Buddhism became a large part of Silla culture. Buddhist monasteries such as the Bulguksa are examples of advanced Korean architecture and Buddhist influence. State-sponsored art and architecture from this period add Hwangnyongsa Temple, Bunhwangsa Temple, and Seokguram Grotto, a World Heritage Site.

Unified 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, near notably during the time of Jang Bogo; in addition, Silla people presents overseas communities in China on the Shandong Peninsula and the mouth of the Yangtze River. Unified 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 numerous 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 offered Mount Jiuhua one of the Four Sacred Mountains of Chinese Buddhism.

Silla began to experience political troubles in the gradual 9th century. This severely weakened Silla and soon thereafter, descendants of the former Baekje established Later Baekje. In the north, rebels revived Goguryeo, beginning the Later Three Kingdoms period.

Unified Silla lasted for 267 years until, under King Gyeongsun, it was annexed by Goryeo in 935.