Excerpts from Books and Wikipedia
"Silla and Balhae coexisted in the south and north of the peninsula, respectively, until 926." [Wikipedia: Timeline of the Middle Ages] "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. . . . 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, 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. Unified Silla was a prosperous and wealthy country, and its metropolitan capital of Gyeongju was the fourth largest city in the world." [Wikipedia]