The bombing of Pearl Harbor on December 7, 1941, ushered the United States into World War II. Within hours, and suspension and martial law came to rule the Hawaiian Territory. On the mainland, the military imposed curfews, designated huge portions of the western United States to be military areas of exclusion, and ultimately created “relocation centers” across the west to detain over 120,000 persons of Japanese ancestry, including over 70,000 citizens. As this chapter explores, in the face of serious constitutional questions about the propriety of martial law, internment of citizens, and military trials of civilians, constitutional considerations generally gave way to war hysteria. But, as many key government actors recognized at the time, the detention of Japanese American citizens violated the Suspension Clause, standing as it did at odds with the entire history of the Clause. As challenges to the relevant military policies spilled over into the courts, the institution arguably best situated to identify and highlight their constitutional infirmities—the Supreme Court—never did so, leaving this episode standing as both a dangerous and deeply problematic precedent in American constitutional history.