Why do you say things went wrong?
Also early Japanese influences ( culture, religin, education, governing the state..) came directly from China and Korea so no they aren't surounded by vast oceans and completely cut off, they decided to be cut off untill the 18./19. century for reasons neither you or I can say are right or wrong.
I also believe in the future North Korea will be the craziest country once it opens up and 100+ years of modern civilisation hits in a day, we'll see fashion, music and every other aspect of urban life go absolutely wild, things happening in Japan will be nothing compared to that