Your answer would be The two countries are strong trading partners.
The United States and South Korea have a very strong relationship between each other, since they both don't like North Korea. The United States is allied with South Korea. Because of the strong bond between them, they must be good trading partners, they can always go to each other for trading purposes due to their close relationship.
I believe it was because of things like segregation and "separate but equal." Even after obtaining citizenship they were still discriminated against by most.
