In some countries around the world, the population that was originally there from the beginning is still there. However, in many others, they are actually a genetic mix. Most of the countries in the Americas are a genetic mix that happened fairly recently according to the timeline of the world. In Europe, many of them are mixtures too. The people in places like Spain and France are not as pure as we think of them as being. The Spanish are a mixture of Romans and Arabs (Moors) who come across the straights between them and Africa and conquered them at one time. France is a combination of Romans and Gaelic people. The English are a combinations of Pic and Saxon (two German tribes), Gaelic, and Roman. The Japanese are a combination of Chinese and Ainu, a kind of Polynesian people. History has been very long.
We are not all as pure as we would like to think we are. As for the Koreans, they have been Korean since the beginning of time, related to the Mongolians. However, when they came down onto the Korean Peninsula, there was some mixing with people from Japan, and there has also been some mixing with China. My Korean son in law can trace his family history back to when they came from China, but they are Korean now. I know a Korean guy in America who did a genetic background test out of curiosity, and he came up about 98% Korean and 2% Japanese.
If you go to Jeju island, directly south of the Korean Peninsula, the people look slightly different from the other Koreans. Their noses are not as round and their lips are not as pudgy. It is because in ancient history, Japanese lived on Jeju Island, and their descendants still carry some of the genetic markers of the Japanese, but they are 100% Korean now.
The larger Koreans are more like what the early Mongolians would have been like, people like Atilla the Hun who almost conquered all of Europe, the big men on horseback. The Japanese are genetically smaller than the Korean race. Many Koreans have it in their heads that they must be small and basically starve themselves to be small because they are oriental, either that, or their parents did it for them. If they eat well, Koreans can get quite big and strong! My Korean son in law was really small as a child because his mother wouldn’t let him eat because he had skin problems, and she thought it came from food. When she took him to the doctor because he wasn’t growing, the doctor said, “Let him eat,” and he grew more than head and shoulders taller than both his parents. Proper nutrition goes a long way. I have seen the same kind of thing happen in other countries.
As for North and South Korea, just a little more than 50 years ago, they were the same country. There are no genetic differences between the two nations. The North Koreans may look smaller because even if they wanted to eat, because of Communism, they are very limited in their food. However, they are genetically the same as S. Koreans, and some S. and N. Koreans are family members, even as close as brothers and sisters, who haven’t seen one another for many, many years because of the separation of the two parts of Korea.
Genetically, there is no difference between N. Koreans and S. Koreans. They are still that race of people who were in ancient times the rulers of the east before China was a power. Korea used to stretch from the Korean Peninsula, up through China, up into Mongolia, and even as far west as into Russia, and they ruled that part of the world for 5,000 years in ancient times. The father of their first king came from the Tower of Babel. They have slowly broken off into smaller groups, but there are still Koreans living in China who speak ancient Korean at home and one of the many Chinese languages when they go out of their house. The Koreans are more homogeneous that most populations on the earth. It was probably caused because after they came to the Korean Peninsula, for thousands of years, they cut themselves off from the outside of the world. They didn’t want anyone to know they were there out of pure self preservation. There had been too many wars, and they didn’t want to fight. If anyone went into Korea, they weren’t allowed to leave so they couldn’t tell anyone where the Koreans were, and Koreans never traveled outside of Korea. The name “Korea” actually came from the time that they were called “Gogoryeo” the huge kingdom that was in power over most of Asia for 5,000 years. They traded along the old Silk Road, a trading route between the east and Europe in ancient times. The people along the Silk Road began calling the country, “Korea.” They call themselves “Hanguk” which means “one country.”
The official name of North Korea is 조선 민주주의 인민공화국 (Joeson meenjoojoo oo-ee eenmeen ho-a gook) meaning “Democratic People’s Republic of Korea.” However, the name 조선 (Joseon) was taken from the period that the Korean Peninsula had three different Kingdoms of the Korean people: Joseon, Bekjae, and Goreyo who eventually became one people again. Joseon was actually around Seoul. Bekjae’s capital was down at Busan. Goreyo was further north in North Korea and up into Manchuria. However, now, the North Koreans have taken the name “Joseon” back.
The official name of S. Korea is 대한민국 (dehan meengook). “Dehan” = great. “Meengook” = nation.