Answer:
To show their loyalty to the US
Step-by-step explanation:
Following the Japanese Imperial Navy's attack on the Pacific Fleet of the United States Navy at Pearl Harbor on December 7, 1941, and the subsequent declaration of US war against Japan, the Franklin D. Roosevelt administration decreed the transfer and seclusion of all of the Japanese residing in the US - including second and third generation, Nisei and Sansei respectively, with US citizenship - for resettlement camps, a euphemised form for concentration camps.
The suspicion that the attack on Pearl Harbor had received the help of Japanese residents in Hawaii and the fear that the citizens of Japanese origin acted as the fifth column justified the creation of these camps.
Since in Hawaii the citizens of Japanese origin made up more than a third of the total population, the measure of incarceration did not have the same rigorous that in the continent. Parallel to the law of internment, the War Department issued an order to license all soldiers of Japanese descent from active military service. Only a few hundred remained in the National Guard of Hawaii. This small group was transferred to a camp in Wisconsin and there had to overcome hundreds of hard tests to demonstrate its value and to swear to die by the USA.