Endo v. United States was a landmark Supreme Court case decided in 1944 that ruled against the internment of Japanese Americans during World War II. The Court held that the government could not detain a citizen without sufficient evidence of disloyalty, emphasizing the importance of individual rights and due process in times of national crisis. This decision played a critical role in challenging the legality of Japanese internment camps and highlighted the consequences of wartime hysteria and racial discrimination.