During the winter of 1942, in the first heated months of America’s war with Japan, the United States government ordered tens of thousands of people of Japanese ancestry, two-thirds of them American citizens, to report to assembly centers throughout the West for transfer to internment camps. The infamous episode has been widely chronicled in books and memoirs, as well as in famous photos by Ansel Adams.

But now close to 800 new images from the period by the photographer Dorothea Lange have been unearthed in the National Archives....