Ancient Korea started out as a community of nomadic people. Eventually, clans began to form, which led to kingdoms. At one point, three rival kingdoms all had equal control over Korea, but one of those kingdoms conquered the other two. The three kingdoms were called the Koguryo Kingdom, the Paekche Kingdom, and the Silla Kingdom. The Silla Kingdom defeated the other two and had complete control over Korea for a little while, but was eventually defeated by the Koryo Dynasty.
China had a HUGE influence on Korea, on everything from religion to currency. Many of the Korean rulers adopted Chinese customs, but added their own rulesThe second part of the website linked below gives a more detailed description of the impacts China had on Korea.
Like mentioned above, the influence China had on Korea was actually an achievement for Korea. Because of it, they were able to spread Chinese cultures, beliefs, and customs to others. Koreans played a part in the spread of Buddhism, and other Chinese religions. Ancient Korea was also responsible for many inventions, everywhere from rocket launchers to heated floors. They created different weapons for their armies, as well as tools for everyday life.
Just like China influenced Korea, Korea had that same effect on Japan. Korean cultures and religions were spread over to Japan, helping to shape a new culture.
During the Koryo period especially, Korean culture thrived. This was considered the "Golden Age" of Ancient Korean history; many new ideas and inventions were created during this time. During this time period, Korean writers carved Buddhist texts into various wooden blocks.