Chinese forces, from the Han Dynasty, attacked and defeated Gojoseon in 108 B.C. Thus began Korea’s long and troubled relationship with China, which still continues to this day. That initial relationship lasted for four centuries through various successive Chinese dynasties. By 313 AD, a new society emerged called Goguryeo which annexed all of the Chinese powers on the peninsula. From there began the ‘Three Kingdoms’ period in Korea. This time in Korea’s history was also the beginning of conflicts between Southern Korea and Northern Korea. The peninsula was briefly unified in the 5th and 6th centuries, and during this period Korean forces defeated Chinese forces for the very first time. The area which is now known as Seoul began to flourish around the 7th century, and Buddhism was also introduced from China which then made its way across the East China Sea to Japan.
Japan was experiencing its own cultural boom in the Heian period (8th to 11th centuries) and evidence shows that much of its culture was influenced by Korea at that time. Japan sent scholars to both China and Korea to learn as much as they could about writing systems, art, Buddhism, and so forth. Goguryeo became Goryeo over time, and this was the precursor to the name Korea. Hence, modern Korean society truly appeared in the 10th century. Buddhism spread throughout the land, laws were established, and the first civil services were initiated. Even the first metal movable type was invented in Korea in the 13th century. However, it still had to defend itself against attacks by Mongolian and Chinese military. Following a successful defense of its territories, a golden era of peace and prosperity began.
Literature, science, religion, education, philosophy and so forth all matured during this period. Wishing to continue development and avoid war, Korea entered into a relationship with Kublai Khan and enjoyed a relatively peaceful friendship with both China and Mongolia. Hanseong (modern-day Seoul) became the capital and many palaces were built. Diplomatic relations and trade began with the Ryukyu Kingdom (Okinawa), Vietnam, Thai (Thailand), Burma, Laos, the Philippines and so on, in addition to China and Mongolia. In the 15th century, King Sejong the Great developed the Korean language, known as Hangul.