The group that was imprisoned under the "internment" policy during WWII was the Japanese Americans.
When WWII broke out, there was a worry in the United States that Japanese Americans might act as spies for the Japanese government.
As a result, President Roosevelt passed an Executive Order that led to Japanese Americans being interned in various parts of the nation as prisoners of sorts.
Find out more on the internment of Japanese Americans at https://brainly.com/question/866534.