The statement that MOST accurately represents the Kingdom of Silla is: The Silla were economically and culturally advanced.
Silla was one of the three kingdoms of Korea and is known for its significant cultural achievements, including advancements in art, architecture, and trade, particularly during its height in the 7th century. The other statements do not accurately reflect the historical context of Silla. For instance, Silla’s military conflicts were primarily with the other Korean kingdoms and not specifically with the Mongols in China, and their government structure was distinct from the Japanese feudal system. Additionally, while Silla's art and architecture were influential, they were primarily centered in Korea rather than throughout China.