My last name is Hyun-woo. I immigrated from Korea a long time ago, but then Korea was divided into north and south. Is there more Hyun-woo in Korea or North Korea now?

I read a book about the history of China, Japanese and Korean. Korean people immigrated from China before. Later, it was divided into Koguryo, Baekje and Silla. Koguryo is the largest country on the Korean peninsula. So I think you are from Koguryo. North Korea and South Korea belong to the same nation. They are one in themselves.