Trump did not simply blurt out that Korea was once part of China. Trump merely quoted what he was told by the President of China.
“Last week, US President Donald Trump said that he had received a 10-minute Chinese-Korean history lesson from Chinese President Xi Jinping during their
first meeting at his Mar-a-Lago resort earlier this month which made him come to the startling realization that the current North Korean crisis is "
not so easy." Apparently though, the lecture also left Trump with a shaky and inflammatory grasp on the region's history.
"[Xi] then went into the history of China and Korea. Not North Korea, Korea. And you know, you’re talking about thousands of years …and many wars. And Korea actually used to be a part of China," Trump
told the
Wall Street Journal last week just before he made his infamous "not so easy" remark.
Trump angers Koreans by saying Korea 'used to be part of China' following history lesson from Xi
It appears that the Chinese President knows a little more about Korean/Chinese history than some of Trumps critics. As it turns out Korea, or at least parts of it, were in fact under Chinese rule a long time ago. The link cited above also provides the following:
“While the history of relations between China and Korea is complicated, including a number of wars and invasions, Koreans generally bristle at the thought that they were ever part of China. For centuries, Korea was part of China's tributary system, paying for protection from its giant neighbor, just like many other kingdoms including Vietnam and Thailand. But parts of Korea were very rarely under anything resembling direct Chinese control -- the notable exceptions being when the Han dynasty set up four "commanderies" in the northern part of Korea in the second century BC and when both were put under Mongol rule in the 13th century AD.”
Another site asks the question: “Was Korea ever part of China?” The answer is complicated but it does appear that at least portions of Korea were part of China for a prolonged period.
“Short answer is a no. More nuanced and subjective answer is a yes, for about 50 years after Mongols subdued Goryeo kingdom. This is subjective because Korea did still have nominal king and he did have absolute authority on Korean peninsula - but this king was almost more a part of Yuan court than an independent king - they were all married into Yuan imperial princesses and even grew up in Yuan court in many cases. Mongols of course aren’t exactly Chinese, so that’s why it’s subjective, if you’re a Chinese person of Mongol descent then the answer is a yes, sort of.
“
The whole of peninsula was never a part of China. Northern part of Korea was part of Han dynasty for roughly 200 years. Han Wudi conquered the northern Korea and parts of Manchuria and set up four commandaries, which is similar to colonial administration” (highlights my own).
https://www.quora.com/Was-Korea-ever-part-of-China
CONCLUSION: Trump was merely saying what the Chinese President told him. Was Trump stupid for relying on what he was told? I don't see it that way. The President of China would be expected to know a lot about the history of his own country and would be considered to be a valuable source of information. I don't consider this to be a major screw up by Trump. I think it was far worse when Obama said Jacksonville, Florida; Savannah, Georgia; and Charleston, South Carolina were in the Gulf of Mexico.
