You are quite unreliable! Seoul is the capital of South Korea. Incheon used to be a small port city, but later it developed into an outer port of Seoul, and now it is a satellite city of Seoul. It is equivalent to the difference between the main city and the outer suburbs. Incheon has been developing badly, only because 1992 has built a new Korean Capital International Airport there, replacing the old Capital International Airport. There is no comparability between the two.