Final answer:
The major breach of civil liberties during WWII was the internment of Japanese Americans following the signing of Executive Order 9066, resulting in the relocation of around 120,000 individuals, most of whom were citizens, to camps with poor conditions.
Step-by-step explanation:
The major exception to the relatively good American civil liberties record during World War II was the harsh treatment of Japanese Americans. Following the attack on Pearl Harbor, there was a widespread fear of sabotage and espionage from those of Japanese descent.
This fear culminated in the signing of Executive Order 9066 by President Franklin D. Roosevelt on February 19, 1942, which led to the forced relocation and internment of roughly 120,000 Japanese Americans, 62 percent of whom were U.S. citizens, into desolate relocation camps.
These internment actions raised serious questions about civil liberties versus national security. Conditions in the camps were poor, with families being separated and individuals losing homes and businesses. Despite some internees showing their loyalty to the United States by complying with the government's orders or even enlisting in the army, the internment is widely regarded as a grave injustice and a significant blemish on America's civil liberties record during the war.