Migrants to Japan have historically received few legal protections under domestic law. Without domestic resources to draw on when fighting discrimination, foreigners and their advocates have drawn extensively, and successfully, on a wide range of international social and legal norms. Specifically, three interrelated types of international norms and laws have been important. First, general, diffuse, non-codified social norms about what it means to be a modern state have been critical in shaping arguments about immigration and immigrant rights. Second, international legal norms, largely written into conventions signed by Japan, have had a direct impact by causing government changes in domestic laws to comply with international legal obligations. Finally, international law has had an indirect, or less direct, impact when lawyers and judges have used various unratified conventions, declarations, and acts of international organisations to interpret domestic law in favour of migrants, even when they do not actually find a practice illegal based on international law.

These three types of international legal and social norms have been critical in extending rights to two groups of foreigners in Japan. Most of the Koreans now living in Japan immigrated, or were forced to immigrate, after the 1910 Japanese annexation of Korea. Koreans were then made citizens, but after the Second World War they were classified as aliens and stripped of their Japanese citizenship. Until the 1965 peace treaty between Korea and Japan, Koreans lived in a state of limbo with no official status and with few remedies for discrimination against them.