Well I am south korean and studying history at university.
But some korean people believe that there was an ancient Korean Empire 10000years ago call 'Hwhan'.
They think this Hwhan empire had occupied total Asia continient, half of the russia, and even America and Europe.
This is really awkward theory and there is no any evidence to prove it. But they said there is evidence.
For example in korea word mother is 'Um- Mah'. So they said this Um mah word changed to 'Amen'. So the even Jesus was Korean :/ And you know, their evidences are total shit.
Fortunately there are no historian accept this stupid Hwhan Empire. They said it's just a trash made by a man who wants to masturbate with fake history.
But some people still believe it is true. And even some senetor of korean argue it is ture history. And they attack normal historians. Because normal historians are jews and japanese who wants to 'hide' their Hwhan empire.
Is there any country have same problem like this?
There is an excellent writeup from /u/commiespaceinvader about a nationalist pseudo-history in Hungary, which claims that the Sumerians became Scythians, Scythians became Hungarians, and also Jesus was a Scythian. Therefore Hungarians are descendants of the inventors of civilization and also Jesus.
It also has some relevant discussion about why these myths can emerge in "lesser" powers like Hungary or Korea, which do not have the same founding myths and ancient lineage as lets say France or China.
If you had not been writing this from Korea, I would have recommended you read Hyung-Il Pai's Constructing "Korean" Origins: A Critical Review of Archaeology, Historiography and Racial Myth in Korean State-Formation Theories.
But yes, these nationalistic, ethnocentric interpretations of history happen all over the world. And it's important to note that these are not new developments either. Scholars were often paid in the past to aggrandize and link their patrons to whichever mythological or historical figure they wished as an ancestor. Geoffrey of Monmouth's The History of the Kings of Britain, which introduced King Arthur to the wider world, was written to provide a history for the Norman conquerors for example.
If you'd like some examples from around the world, I recommend the book edited by Kohl and Fawcett Nationalism, Politics and the Practice of Archaeology.
I think this counts
There were a sizable amount of pro-slavery individuals/slave owners that justified their belief that Africans should/deserved to be enslaved because they claimed that africans were 'descended from cain' and thus this was their punishment from god, that their souls were tainted etc