"Sangokujin" means The third nation in Japanese. After Japan surrendered the war, Korean & Taiwan Japanese felt shame to hold the lost contry's citizenship, and claim GHQ to be Korean or Taiwanese. In the fact, Korea and Taiwan hadn't existed during the war, therefore GHQ named them "The Third Nation" - Neither won/lost country- and it's the root of "Sankokujin".
Since GHQ agreed them not to be Japanese, the Japanese police had no rights to arrest them. These "Sankokujin" had been bully, opened illigal business and even murdered Japanese all time. These reality created fears to Japanese citizens toward "Sangokujin". "Sangokujin" has been the symbol of agressive and bully foreign people in Japan, and it's not discriminatory tariffs at all.
Today, the governor of Tokyo said the term "Sangokujin" in the public and it had been causing troubles. Some Koreans clamed him that he should appapologize about spoke such a discriminatory term in the public. However the fact of the matter is, "Sangokujin" had been spoken as the illigal foreign people who may fear others. Therefore, using the term "Sangokujin" is not discriminatory. These Koreans claimed because their hatreds of the governor who trys to eliminate illigal foreigner from Tokyo.