In Nishikawa v. Dulles, the U.S Supreme Court ruled in favor of a Japanese-American dual citizen who was accused by the State Department of voluntarily renouncing his American citizenship during World War II while serving in Japan's military. The court held that when an individual is claimed to have lost their U.S. nationality due to service in foreign armed forces, it must be proven beyond reasonable doubt that such service was voluntary and not under duress or coercion. The burden of proof lies with the government rather than on the individual to prove they did not act voluntarily. This case set a precedent for future cases involving loss of nationality due to alleged disloyalty or treasonous acts.

In the dissenting opinion for Nishikawa v. Dulles, Justice Frankfurter argued that the majority's decision undermined a key principle of international law: dual nationality individuals must bear the responsibilities of each citizenship. He believed that Mr. Nishikawa willingly served in Japan's military during World War II and should therefore be held accountable for his actions as a Japanese citizen, despite also holding American citizenship. The justice disagreed with the majority’s view that duress had been established without requiring proof from Nishikawa himself; he contended this shifted an unfair burden onto government to disprove claims of coercion in all similar cases going forward. Furthermore, he criticized their interpretation of Section 401 (c) of Nationality Act as overly broad and inconsistent with its legislative history and intent.