I'm afraid to go into a dangerous path of looking into one's own roots and expressing openly his own view in this time of prevalent prejudices. But some people may want to know what would be my view of it all.
Historically, Koreans tend to distance themselves from the Manchus and the Hyung-nos(Huns) as they were considered nomadic horse riding barbarians who do not know how to discuss the Confucian philosophy using the highly sophisticated Chinese hieroglyphs. It can not be overlooked that Koreans aligned themselves with the Han Chinese as being educated and civilized compared to their more immediate kins of the northern Asia. So you can see there was a great deal of pretentiousness on the part of the so called scholars in the ancient Korean society.
One of the interesting observations in this respect is that Chinese called ancient Koreans "Dong Yi" meaning "The Eastern Tribe riding on a horse carrying a bow and arrows". The Chinese hieroglyphs "Yi" depicts a person riding on a horse with a bow and arrow. So, basically what it means is that the ancient Koreans were also viewed by Chinese as a nomadic horse riding people not much different than Huns(Hyung No) and Manchus, until they settled down in the peninsula to form an agricultural society. In fact, the famous Chinese historian "Sa Ma Chon" wrote in his book "Sa Ki" that Confucius was from "Dong Yi". More specifically it is the area of the present day San dong peninsula which belonged to the proto Koreans in ancient times. When Chin Si Huang Di unified the greater China, Sandong and Manchu were not part of it. Later Sandong people conquered China, expanded its territory and established Han dynasty. The sound Han is the same as that of Hun and Han of ancient Koreans who shared the Tungusic language. The correct sound of Han, Hun is "Kheun" in the present day Korean language which means "Big" and "Great". Obviously, Hun people liked to call their country "great" whenever they built one. So it was Dongyi people who ruled the greater China in Han dynasty. We will see again that Manchus will conquer China and establish Qing dynasty. This is a repeated pattern showing how the historical China has been formed.
At the end of Koryo dynasty, the last King of Koryo ordered his general Yi Sung Gae to attack Manchuria to punish them for destroying Ming dynasty, our beloved Chinese friends. It is the spirit of Koryo dynasty that attracts the special attention. "Orangke" which Koreans called Manchus means savage barbarians.
Sadly, general Yi Sung Gae returned from his post and took the crown and established Chosun(Yi) dynasty. Some may think he was a hero but he was a traitor to his people in a deeper sense. Jeong Mong Ju was the last scholar of Koryo dynasty who opposed general Yi and paid the ultimate price. He was the last honorable scholar of Koryo dynasty who chose the loyalty and principle over the power and wealth. Because he was promised by Yi Sung Gae the greatest role in the new dynasty if he had cooperated. The triumphant spirit of the great Koryo people was ruthlessly mutilated by Yi Sung Gae and his ensuing dynasty, which has wasted most of their time and energy debating on the worthless subject like how many days the sons have to show remorse when their parents or the Kings were deceased, when Japanese were diligently developing the modern technology. The deadly trap of the Confucian philosophy is in the fact that it emphasizes too heavily on how you will be looked at by others in your behavior than how you truly feel inside of yourself. It may be called a philosophy of teaching the most sophisticated pretentiousness in life. But it certainly has its greatest merit which can not be ignored like the strong emphasis on learning. The book of Confucius starts with the saying "Isn't it the most joyful thing to learn and practice every day?" Of course, it depends on what you learn.
Basically, Yi dynasty was fearful of the fact that some military general may revolt and take their dynasty away from them and subsequently neglected in building up the military and technology for the self defense of the nation. Their sins were their worst enemy. As a consequence, Chosun dynasty left the lasting impression of being a timid nation to Japan and China vulnerable to their attacks.
The major reason for this observation that the Manchus and the Huns were more close to Koreans is in the language they use if not the completely identical physical features. The so called Tungstic language which is also called Hunnic language is unique in the sense that the majority of the languages in the world are not like it in terms of the particular grammatical structures. It is known that the Turkish and the Hungarians share the same structure of the language. Unless you have learned any one of these languages, you have no idea how different the Hunnic language is.
The fact that Koreans, Mongols, Japanese, Hungarians and Turkish share this particular kind of the structure of the language is no coincidence. It depicts the trail of the migration and spread of the Hunnic people.
In fact, Manchuria was a greater part of Korean territory in ancient times as admitted by the main stream Chinese history. But it wouldn't be fair to say that Koreans lost that part of the land to China in a war. Instead, in later part of the history, Manchus conquered the mainland of China and separated themselves from the rest of the Koreans and included their land of Manchuria to the rest of the China and established Qing dynasty.
It is not very well publicized fact but it is well worth to note that the Chinese language is more close to Europeans than that of Koreans. It belongs to a part of the so called Indo-European language group. In this particular language group, which is shared by the majority of the languages in the world, the order of the words placed in a sentence is very important while in Tungustic language, they have distinctive sounds that attached to the words specifying if the word is a subject, an object or a verb, which makes the meaning of the sentence very clear even when the order of the words are all shuffled around.
Somehow the Manchurians totally assimilated their grammatical structure of the language into Chinese. But in terms of the pronunciation of the individual Chinese letter system, the Mandarin(standard Chinese spoken language originated from Manchus) pronunciation is more close to that of Koreans than that of Cantonese as one would naturally expect.
As is well known more from the European history, the Huns(Hyungnos)(Chinese built the great wall to protect themselves from the Huns) in the 4th century conquered most part of the Europe and contributed to the ultimate fall of the Rome. The Hunnic people settled down in the modern day great plain field of Budapest Hungary. So, it is not surprising to see that Hungarians speak Hunnic language to this day. The majority of the women Huns brought with them must have settled down there to influence the mother tongue of the whole country. No wonder Europeans have been wondering why Hungarian language is so difficult to learn. The modern day Hungarians do not hide the fact that their ancestors were Huns. Also they are very proud of naming their sons by the name Attila to the chagrin of their heavily Rome influenced neighbors. Still it must be noted that the King Attila the Hun had many children from many of his wives, who inherited his vast conquered Kingdoms in Europe. It is not surprising to see that King Charlemagne is considered one of his descendants.
The historical role of Yamato faction in Japan must also be noted, which is very interesting. Korean history writes that the ancient Baikje kingdom of Korea(south west of the peninsula) had their colony in Japan 1500 years ago. Coincidentally, the last general of Baikje Kingdom, Gae Baik, killed himself like in the Samurai tradition, cutting his own stomach with a sword and killing all of his family(to prevent them from being humiliated by the enemy) upon taking the responsibility of failing to protect his country. The royal family of Baikje kingdom sailed to Japan after the fall of the country by Shilla(south east of the peninsula) and Chinese(Tang dynasty) coalition force. Considering that the written Japanese history starts about this time, it can be concluded that Baikje dynasty was at the core of the unification of the countless Japanese islanders and the establishment of the emperor family which lasted ever since. Most of the core historical tradition of Japanese culture was originated from Baikje kingdom and obviously the Samurai tradition was one of them.
From the far west of Europe to the far east of Japan, Hunnic people left their foot prints and the strongest political and social influences. And of course, those countries have become the major super powers of the modern world. This can hardly be a coincidence.
One may be able to find the deeper root of the meaning of it from the following observation. Nothern Europeans never formed a unified front against Rome before the Hun's invasion of Europe in the 4th century AD. Japanese islanders couldn't be unified before the Yamato faction mobilized by the Baikje kingdom unified them all. Without Baikje's intervention, Japan could have been left pretty much like the modern day Phillipine which doesn't seem to have the core soul of the nation, allowing the constant insurgent of the regional terrorist groups to this day. One can not imagine this kind of disorderly disturbances to happen in any of their islands in Japan.
The Hunnic people in the early history of mankind provided the source of the strong central government to the people of the land they conquered. And they faded away, at least it seemed they did until someone mentions of their monumental achievements. The human civilization could not have flourished without this pivotal central social mechanism. One can own a property only of the size they can visualize and reach. Clearly, the early Hunnic people had the bigger visions of it and the means to reach there.