Final answer:
The central idea of the Supreme Court's majority opinion in Korematsu v. United States was that national security needs during World War II justified the internment of Japanese Americans, which trumped individual civil liberties.
Step-by-step explanation:
The central idea of the majority opinion in Korematsu v. United States was that the need to protect against espionage outweighed Fred Korematsu's individual rights during World War II. The Supreme Court upheld the legality of the internment of Japanese Americans as a wartime necessity. This case highlighted the balance between national security and civil liberties, with the Court granting significant deference to the executive branch under the war powers granted by the Constitution.
In the Korematsu v. United States case, the Supreme Court ruled in a 6-3 decision that the internment of Japanese Americans, authorized by President Roosevelt's Executive Order 9066, did not violate the due process rights of those interned. The central justification for the Court's decision was national security, asserting that the potential threat of espionage by persons of Japanese ancestry justified the abrogation of individual rights. This decision has been heavily criticized for its stance on civil liberties and its institutionalized discrimination based on ethnicity. Over time, with new evidence and changing perspectives, the decision in Korematsu has been acknowledged by various government entities, including the Supreme Court itself, as erroneous. Nonetheless, the Korematsu decision remains as a pivotal example of the extent of presidential war powers and the potential limitations of constitutional checks on executive power.