third country's citizen) is a Japanese term referring to the various former colonial subjects of the Empire of Japan in the aftermath of World War II.
This resulted in many underprivileged Taiwanese and Korean people previously living under colonial rule forming criminal gangs such as the Yamiichi (闇市), a black market which was against the rationing system which continued after the war.
However, the use of the term was revived when the nationalist Tokyo Metropolitan Governor Shintaro Ishihara used it in an April 9, 2000 address to the Japanese Self Defense Forces (JSDF).
In the speech, Ishihara suggested that the JSDF would be needed to suppress Sangokujin criminal activity in the event of a catastrophic disaster in Tokyo.
This provoked discussion about the political correctness of the term and whether or not colonialism of Korea and Taiwan is by itself an act of robbery of resources and native cultures.