South Korea on Thursday clarified that it was never a part of China, after President Donald Trump told The Wall Street Journal that Chinese President Xi Jinping told him that “Korea actually used to be a part of China.” Cho June-hyuck, a spokesman for South Korea’s foreign ministry, said “it’s a clear fact acknowledged by the international community that, for thousands of years in history, Korea has never been part of China.” Hong Joon-pyo, a South Korean presidential candidate called the suggestion a “distortion of history” and “an invasion of the Republic of Korea’s sovereignty.” The comment comes amid an already-tenuous relationship between South Korea and China over the U.S.’s deployment of a missile defense system in South Korea in an effort to counter North Korean aggression.
Korea become a tributary state of Manchu in 1637, with its status continuing under the Qing dynasty until 1894. As for why Korea never remained a part of China, it was incredibly difficult to conquer. The Korean peninsula is mountainous, which made it highly defensible.
Don't take my words for factcheck it yourself!
Note to self: Feb 8 - FBI Anon Leak on Brennan & Comey indictments becoming public...+6