Hi!!

I am a high school student in Korea and my name is Ashley -Ji

Are you aware of the correct meaning of 'vassal' ?
If you know the meaning of this word and use it properly, you may not understand the history of Asia correctly because:

Historically, Korea has never been a subordinate country of other countries. It has continued to trade and exchange with other countries, including China and Japan. This trade is a legitimate exchange between countries and is not a tribute. This should not be understood as a relationship of assumption that could happen to the feudal states of Europe.

 The second is that Korea has a historically independent leader. That is why it has proudly brought about a meeting of leaders in its relations with other countries. kIing of many generations worked for Korea's interests and were independent beings who were not ruled by other countries and handed over their power to the next generation.

Thirdly, Korea has a unique Korean culture. It varies across languages and cultures, including the letters 'hangeul'.
In particular, Han-gul is famous for being more original and scientific than any other country in the world. Now, many people in the world want to learn and write this language.
It is made by Koreans in a convenient and appropriate way for the language they use.

Therefore, Korea has never been ruled by any country in history.